Reflection Processing and Analysis

1. Shallow Subsurface Investigation across many areas of the V-line and Truckee Canal Fallon, Nevada Reflection Processing and Analysis Bryce Grimm Mayo Thompson

2. Overview Introduction Reflection Parameters Analysis of Reflection Lines (FALL0101 & FALL201-336) Comparison with other methods Conclusions

3. Introduction • This project involved the use of five (5) geophysical methods across the V Canal and the Truckee Canal in order to identify the shallow subsurface geometry of these areas. • We conducted the reflection portion of this project and the following is the analysis, results and comparison

4. Reflection Parameters • Refraction was first conducted which helped us to decide our parameters for collection. • 2 lines were conducted: one at the TCID power plant along the same line as ReMi line # 1; the other Southwest of TCID at a part of the levee at a lower height (ReMi line # 3) • We used a .2 ms sample rate, 1000 samples per shot, and 10 shots per shot point.

5. Reflection Parameters FALL 0101 – TCID power plant • Bison Galileo 21 Seismograph • The line was setup as such: • 24 channels • Group spacing of 0.7 meters • Shot spacing of 1.4 meters • 30 Shots (1 for each geophone group and 3 shot 1.4 meters out from the both ends. • Placed linearly along array

6. FALL0101 • The program used to analyze this data was jrg500 • First picks were made on the initial reflections to access initial velocities, frequency, and resolutions.

7. FALL0101

8. FALL0101 – CVSTACK • After applying geometry, a band-pass filter of 50-75, 250-300 Hz, trace equalization gain and also an automatic gain control, constant velocity stacking was assessed to identify the ideal parameters. • The final parameters came to be: 100 m/s with 24 intervals of 20 m/s.

9. FALL0101 – CVSTACK

10. CMPSTACK AND MAKEVELS • Velocities vary from 200-500 m/s in the shallow layers and 900 m/s at the deepest layer. • Depth to the bottom of the levee is 3.3 ± .75 m Bottom of levee 3.3 m High velocity pocket

11. CMPSTACK AND MAKEVELS • The high velocity pocket seen in the results correlated with a note made on the observers report very well. • The beginning of the pocket is at about 9 meters and we noted that past 7 meters the soil was more compact causing the plate to bounce. The dirt became softer later on in the survey. • Therefore a small higher velocity layer is feasible. Bottom of levee 3.3 m High velocity pocket

12. Reflection Parameters FALL 201-336 – • Bison Galileo 21 Seismograph • The line was setup as such: • 48 channels • Group spacing of 0.35 meters • Shot spacing of 0.7 meters • 36 Shots (1 for every other geophone group and 6 shots 0.7 meters out from the both ends. • Each group placed was placed with 3 geophones linear to array and 3 perpendicular to the array as shown.

13. FALL201-336 • The program used to analyze this data was also jrg500 • First picks were made on the initial reflections to access initial velocities, frequency, and resolutions.

14. FALL201-336

15. FALL201-336 – CVSTACK • After applying geometry, a band-pass filter of 50-75, 250-300 Hz, trace equalization gain and also an automatic gain control, constant velocity stacking was assessed to identify the ideal parameters. • The final parameters came to be: 100 m/s with 24 intervals of 20 m/s. This was the same as the first line. • We decided to use the same parameters because (1) the energy was still constrained and (2) keeping the same parameters ensured similar results.

16. FALL201-336 – CVSTACK

17. CMPSTACK AND MAKEVELS • More linear results and not much is seen. • Velocities vary from 100-400 m/s in the shallow layers. • The bottom of the levee is about 2.15 ± .47 m • Middle area has higher fold due to merging of lines

18. CMPSTACK AND MAKEVELS • Although the results for this line were less interesting, they do essentially show the linear and clear break between the canal and the natural surface.

19. Comparison with other methods - ReMi • Line 1 was the same amount of geophones conducted with the same starting point as FALL0101. ReMi had a geophone spacing of two times the length of the reflection geophone groups (1.4 meters compared to 0.7 meters) • The canal bank depth determination for this method was 2.5 ± .5 meters while reflection yielded a depth of 3.3 ± .75 meters, a difference of 14%. ReMi inherently has a 20% error (Heath et. al., 2006) and the vertical resolution was about 20%. Therefore the depth to the bottom of the levee is constrained by 2.55 – 3.00 meters. • Next, in terms of velocities, the reflection velocities of the levee were between 200-500 m/s and shear velocities varied from 150-185 m/s. • Because shear waves are 60% of reflection waves, ideal shear wave velocities are between 140 – 300 m/s which fit perfectly with the results shown.

20. Comparison with other methods - ReMi • Line 3 was 24 geophones conducted with the same starting point as FALL201-336 • which was 48 geophone groups. ReMi had a geophone spacing of four times the length of our survey (1.4 meters compared to 0.35 meters) • The canal bank depth determination for this method was 2.3 ± .46 meters while reflection yielded a depth of 2.15 ± .47 meters. Remi inherently has a 20% error (Heath et. Al, 2006) and the vertical resolution was about 20%. Therefore the depth to the bottom of the levee is constrained by 1.84 – 2.61 meters. • Next, in terms of velocities, the reflection velocities of the levee were between 100-400 m/s and shear velocities varied from 150 - 190 m/s. • Because shear waves are 60% of reflection waves, ideal shear wave velocities are between 80 – 240 m/s which fit perfectly with the results shown.

21. Comparison with other methods - Refraction • Refraction line 1 coincides with FALL0101. It has a canal depth of 2.3 m but an interpretation can range from 1.0-3.0 m and velocities ranging from 200-500 m/s. • This is a bit lower in depth than the reflection results but depth ranges fit into the depth calculated as 2.55-3.00 although the velocities match.

22. Comparison with other methods - Refraction • Refraction line 3 coincides with FALL201-336 and has a canal depth of 2.5 m. The interpretation ranges from 1.0-3.0 m and velocities ranging from 200-700 m/s. • This matches with the reflection data, falling into the range of reflection depths of 1.84 – 2.61 m but is higher in velocity than the 100-400 m/s resulted.

23. Comparison with other methods – Electrical Resistivity • The only electrical survey conducted was on the line FALL201-336. • The calculated depth to native soil varied from 2.5 – 3.1 meters

24. Comparison with other methods – Electrical Resistivity • The only electrical survey conducted was on the line FALL201-336. • The calculated depth to native soil varied from 2.5 – 3.1 meters

25. Conclusions – FALL0101 • Given the reflection results and two comparative methods (ReMi and Refraction), the depth to bottom of levee is between 2.5 – 3.0 meters with velocities of 200-500 m/s. • Conducting resistivity in this area might have narrowed the depth of the canal

26. Conclusions – FALL201-336 • Given the reflection results and three comparative methods (ReMi, Refraction and Electrical), the depth to bottom of levee is between 2.5 – 2.6 meters with velocities of 200-400 m/s when using the constraints of each process.

27. THE END • QUESTIONS??? References: Heath, K., J. N. Louie, G. Biasi, A. Pancha, and S. K. Pullammanappallil, 2006, Blind tests of refraction microtremor analysis against synthetics and borehole data: CD-ROM Proceedings of the 100th Anniversary Earthquake Conference.