1. GRAVITY in Yosemite Valley
MICHELLE DUNN
JORDAN BARKER
CHEYENNE LAWRENCE
PHILLIP ZURN

2. LaCoste and Romberg G509 A relative gravimeter
Gravimeter measures local gravitational field of the Earth
Susceptible to vibrations due to sensitivity
Voltage > 12.0v
2 hour loop for drift correction
GPS assist

3. Methods - Data Collection
Stable paved or rocky location
Center the Long and Cross Levels using the adjustment knobs
Unlock arrestment knob
Gravity reading is taken once the cross hair in the light beam settles on 3.2
Reading is taken to two decimal places

4. Yosemite Valley Transects on March 19th - 21st

5. Methods - Corrections Drift Elevation Correction Terrain Instrument
Tidal
Elevation Correction
Free-Air
Bouguer Slab
Terrain
Inner: SBA
Outer: CBA

6. Zone BCDEF Inner Terrain Correction

7. Outer Terrain Correction

8. Outer Terrain Corrections: QCTool
Input lidar file as csv
Obtain easting and northing
Input DEM - GTOPO30
Resolution 30 arc second
Output terrain corrections

9. Simple Bouguer Anomaly vs Latitude

10. SBA vs Latitude for Transect 2

11. SBA vs Longitude W E

12. Depth vs Latitude S N S N

13. Depth vs Latitude for Transect 2
⍴ = -0.5 g/cc
⍴ = -0.7 g/cc S N S N

14. Depth vs Latitude

15. Gravity Uncertainties
Lies primarily with terrain corrections
Terrain correction: 4.5 mGal
Uncertainty in basin thickness assuming ⍴ = -0.7 g/cc: 150 meters
Uncertainties due to lack of knowledge of basin densities
Using Gutenberg max depth of 600 m, ⍴= g/cc
Sierra Granite ⍴=2.67 g/cc, not realistic to have basin sediment < 2.0 g/cc

16. Conclusions and Future Work
“Double camel” geometry with deepest point under El Capitan
Constrain density contrast
Validation of terrain correction with other DEM or 3D modeling of lidar
Absolute gravity calculation
Comparison with ReMi and resistivity data

17. References
Gutenberg, Beno, John P. Buwalda, and Robert P. Sharp. "Seismic explorations on the floor of Yosemite Valley, California." Geological Society of America Bulletin 67.8 (1956):
Telford, William Murray, Lloyd P. Geldart, and Robert E. Sheriff. Applied geophysics. Vol. 1. Cambridge university press, 1990.
Louie, John. "GPH 492." GPH 492/692 - Applied Geophysics. N.p., n.d. Web. 09 May 2017.
Huber, N. King, Paul C. Bateman, and Clyde Wahrhaftig. Geologic map of Yosemite National Park and vicinity, California. No