1. Seismic Refraction Analysis of California Wash and Astor Pass
Stephen Hein
Mason Kreidler
Nina

2. Overview Project Objectives Field methods Analyses Interpretations
Discussions
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3. Project Objectives California Wash Astor Pass
Analyze the fault running through California Wash, to evaluate seismic hazards for Las Vegas
Astor Pass
Examine regions that were not previously drilled, to see if more promising geophysical prospects exist
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4. Equipment: All lines 7 kg sledgehammer 100 Hz Geophones
Seismic source
100 Hz Geophones
Seismic vibration monitor
Seismic cable with 48 channel
Data transfer
Bison Galileo-21
Data logger
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5. Analysis: All lines First arrival picks using Viewmat
Better images through Band-Pass filters, TEGain,
Simple calculations using a time-distance plot in excel
V1 and V2 velocities:
Refractor depth:
Dip angle
Estimated low and high velocities
Possible third layers

6. Analysis: All lines
Dr. Pullammanappallil created P-wave seismic velocity sections from our first-arrival pick times using ( 2011 Optim)
Cross Section with velocities
Refractor depths
Layer velocities

7. Field Methods: California Wash Line 1
Seismic cable oriented East-West with a total length of 100 meters
2 meter spacing between each takeout
6 geophones per takeout oriented parallel to the seismic cable
Sledgehammer hits used to propagate waves into the ground
10 hammer hits at each source point
A total of 74 source points were taken
14 to the East of the first geophone at a spacing of 4 meters
48 at each channel along the line
12 to the West of the last geophone at a spacing of 4 meters
Total length of hammer hits: 200 meters
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8. Layout of seismic cable and geophones (Louie, 2011)
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Layout of seismic cable and geophones (Louie, 2011)
Producing waves using a sledgehammer and layout of geophones (Louie, 2011

9. Results: California Wash Line 1
V1: m/s with an average of m/s
V2: m/s
Refractor depth between m
Dip angle of 1.3 degrees

10. Optim's SeisOpt®@2DTM Results: California Wash Line 1

11. SeisOpt® Interpretation: California Wash Line1
P-Wave velocity was m/s, consistent with simple calculations average of 880 m/s
V2 of ~ 1400 m/s consistent with simple calculations
Estimated refractor depth of 1-10 m, also consistent
Very low eastward dip in first refractor

12. Field Methods: California Wash Line 2
Seismic cable oriented East-West with a total length of 48 meters
1 meter spacing between each takeout
6 geophones per takeout oriented perpendicular to the seismic cable
Sledgehammer hits used to propagate waves into the ground
10 hammer hits at each source point
A total of 48 source points were taken
48 at each channel along the line
Total length of hammer hits: 48 meters
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13. Example of geophone arrangement and wave propagation at line 2 (Louie, 2011)

14. Results: California Wash Line 2
V1: m/s with an average of m/s
V2: m/s
Refractor depth between m
Dip angle of degrees

15. Optim's SeisOpt®@2DTM Results: California Wash Line 2

16. SeisOpt® Interpretation: California Wash Line2
P-Wave velocity was m/s, consistent with simple calculations average of 270 m/s
V2 of ~ 1200 m/s consistent with simple calculations
Estimated refractor depth of 1-2 m, slightly higher than estimated in simple calculations
Minimal evidence of any dip in the first refractor

17. Interpretation of California Wash Lines 1 and 2
Conformation of good results by overlaying CW2 onto CW1

18. Discussion: California Wash Lines 1 and 2
Results from Line 1 give a good indication of the dip of the fault running through the wash
Line 2 shows evidence of the amount of slip that occurred that last time on this fault, by the amount of recent, slower velocity, sediment on top of older, higher velocity alluvium

19. Field Methods: Astor Pass
Seismic cable oriented East-West with a total length of 144 meters
3 meter spacing between each takeout
6 geophones per takeout oriented parallel to the seismic cable
Sledgehammer hits used to propagate waves into the ground
10 hammer hits at each source point
A total of 60 source points were taken
48 at each channel along the line
12 to the West of the last geophone, at a spacing of 6 meters
Total length of hammer hits: 220 meters
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20. Layout of seismic cables and geophones at Astor Pass
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Layout of seismic cables and geophones at Astor Pass

21. Results: Astor Pass V1 of 275-400 m/s with an average of 337.5 m/s
Refractor depth between m
Dip angle of 1-5 degrees

22. Optim's SeisOpt®@2DTM Results: Astor Pass

23. SeisOpt® Interpretation: Astor Pass
P-Wave velocity was m/s, consistent with simple calculations of m/s
V2 of ~ 1000 m/s consistent with simple calculations of 1090
Estimated refractor depth of m, also consistent with previous calculations
No dip in first refractor

24. Basic Interpretation

25. Discussion: Astor Pass
Results from SeisOpt® did not agree with the hypothesis of seeing faster velocities near the middle of the plot where tufa layers were thought to exist.
These results actually lean towards a hypothesis that most if not all of the tufa is already on the surface.

26. Possible Sources of Errors
Wind creating noise on the seismic line.
People walking around on the seismic line while recording data.
First arrival picks may have been off slightly; however, refractor depth and data was consistent throughout the plot, suggesting picks were valid.

27. Conclusion of Astor Pass
Refraction Microtremor results agreed with our Refraction results of not seeing faster velocities near the tufa mounds.