Loading in 5 sec....

Gravity in the Fernley & Hazen Flat AreasPowerPoint Presentation

Gravity in the Fernley & Hazen Flat Areas

- 77 Views
- Uploaded on

Download Presentation
## PowerPoint Slideshow about ' Gravity in the Fernley & Hazen Flat Areas' - nadine-beasley

**An Image/Link below is provided (as is) to download presentation**

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript

### Gravity in the Fernley & Hazen Flat Areas

Geol 492/692 Spring 2005

Melissa Edwards, Harmony Farnsworth, and Rich Redd

Methods—Gravimeter

- Used a LaCoste & Romberg Model G Gravimeter to measure gravity at each location
- Before each trip to the field a base station measurement was taken at UNR outside of SEM (Base 1)
- At both the Fernley and Hazen sites a base station was established and a gravity measurement was taken the morning, afternoon, and the evening of each trip (Base 2 & Base 3)
- The base station gravity measurements were all within 0.5 mGals of each other, indicating the gravimeter was working correctly

- A calibration correction for the reading for the gravimeter was made using one of the following formulas (depending on what the gravity reading was):
- For 3100 reading: ((Gravimeter reading-3100)*1.02258)+3170.62
- For 3200 reading: ((Gravimeter reading-3200)*1.0226)+3272.88

Methods—Trimble

- Used a Trimble XT GPS to measure elevation and lat/long at every location
- Instrument was placed 10 ft or less away from the spot where a gravity reading was taken, but at the same elevation level
- Instrument was allowed to collect GPS points for 10 minutes or 120 points, which ever came first

- Data
- Downloaded using GPS Pathfinder Office 3.0
- Used the Reno airport as the reference for corrections to all the GPS data collected from the Trimble since it had data for all the days we recorded.
- Horizontal error at least 6 cm.
- 68% confident elevation is within 2 meters
- Amounts to a 0.3 to 0.6 mGal error in the Bouguer calculations

Methods—Terrain Corrections

- Estimations were made of the elevation difference b/w the place where the gravity reading was taken and the surrounding topography
- For zone B (6.56’-54.6’), 4 directions
- For zone C (54.6’-175’), 6 directions

- With these values a chart was used to find the dgr values for each direction & all of these values were added to obtain the total terrain correction value

Methods—Bouguer Correction

- Bouguer anomaly value calculations were made using the gravity readings from the gravimeter, the terrain corrections, the elevation/lat/long data downloaded from the Trimble, and the following formulas:
- Free Air Correction = 0.3086 * elevation
- Bouguer Correction = 0.0419*density (used 2.67) * elevation
- Theoretical Gravity = 978.03185* (1 + (0.0053024 * sin2 (latitude)) – (0.0000058 * sin2 (2 * latitude))
- Bouguer Anomaly = (Observed Gravity + Free Air Correction – Bouguer Correction) – Theoretical Gravity

Methods & Results—Fernley Line 1

- Gravimeter points were spaced 100 meters apart
- Points S1-S19 were surveyed (plus Base 1 & Base 2)

Methods & Results—Fernley Line 2

- Gravimeter points spaced 100 meters apart
- Points S201-S221 were surveyed (plus Base 1 & Base 2)
- Poor satellite coverage for S204 & S205 with the Trimble

Methods & Results—Hazen

- Gravimeter points were spaced 100 meters apart
- S128 was spaced 150 meters form S127
- S131 was spaced 330 meters from S130

- Points S100-S131 were surveyed
- Poor satellite coverage for S121 & S122 with the Trimble

Modeling—Bouguer Slab Depths

- Where Δg= The computed Ganom value from grav2d
- Δρ= -.35
- The 0.0419 value is a constant

Bouguer Slab Equation (Telford et. Al.1990)

Fernley 1

Blue lines indicate regional stresses. Red lines indicate shearing within the flower structure

Download Presentation

Connecting to Server..