1. A Seismic Survey Across a Suspected Fault in Mason Valley, Nevada Camille Amdall , Ian Pierce, Kate Curtin, Eric, Conner, Amanda, Lauren, somebody, John N. Louie GPH 492/692 Applied Geophysics class 2017, University of Nevada Reno
Refraction Analysis
Reflection Analysis
Example refraction record with 1st-arrival picks:

2. Background Conducted March 23, 2017 in Mason Valley, NV
Objective: identify and characterize the “Little Mason Fault” discovered by Ian Pierce of UNR
Two seismic reflection-refraction lines with 48 channels each
Survey lines were east-west-trending
3 m spacing between each channel with groups of six 100 Hz geophones
A plate and a 16 lb sledge hammer provided the seismic source, 10 hits per flag
A Bison recorder saved all of the data generated by the geophones
Seismic processing with Louie’s free JRG/Viewmat software from crack.seismo.unr.edu/jrg

3. Reflection
Filter tests showed prominent reflections between Hz
Constant-velocity stacks testing velocities from 500 to 2500 m/s
CMP stacking with velocities picked for maximum continuity on the CV stacks
Fault breaks identified on the CMP stack at the apex of diffraction hyperbolas
Post-stack Stolt migration at 1700 m/s collapses diffractions to show stratigraphy better

4. Refraction
The velocity of a wave is dependent on the stiffness of the rocks through which it travels
Some channels were missing due to problems with the instrumentation (bad cables, geophones not plugged in)
In an area where the geology is composed of discrete homogenous layers modeling can be quite easy. Mason Valley offered a much more complicated geological environment
Refraction analysis required optimization of first-arrival travel times with SeisOpt® @2d™ from Optim, a sophisticated velocity tomography
First-arrival picks are being reworked for LMF2, to verify the large discontinuities in the P-velocity section
The LMF1 P-velocity section suggests velocities are lower uphill of the fault- Why?

5. Data Processing
3 steps
application of array geometry to all of the raw data
we picked the first p-wave arrivals using Dr. John Louie’s viewmat application
exporting all of the data to
Problems
1. Due to the geology of the site and the relatively small amount of energy released by the source, this presented a difficult task requiring the use of automatic gain control to “normalize” the records and increase the visibility of faint first arrivals.
2. Some channels were missing due to physical problems with the instrumentation (not plugged in)