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

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

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

Yosemite Valley Transects on March 19th - 21st

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

Zone BCDEF Inner Terrain Correction

Outer Terrain Correction

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

Simple Bouguer Anomaly vs Latitude

SBA vs Latitude for Transect 2

SBA vs Longitude W E

Depth vs Latitude S N S N

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

Depth vs Latitude

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, ⍴=-0.945 g/cc Sierra Granite ⍴=2.67 g/cc, not realistic to have basin sediment < 2.0 g/cc

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

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): 1051-1078. 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. 1874. 1989.