1. Ground-roll Inversion for Near-surface Shear-Wave Velocityby
Soumya Roy, Graduate Student
Department of Earth and Atmospheric Sciences
University of Houston

2. 1. Introduction
2. Multichannel Analysis of Surface Wave
(MASW) in Nutshell
3. MASW Analysis of Seismic Data
- La Marque, Tx
4. Results and Interpretation
5. Future Avenues

3. Introduction
Estimating a near-surface S-wave velocity (Vs) structure is important
Provide static solution for multi-component seismic analysis
Ground Roll inversion can provide near-surface Vs solution
Multichannel Analysis of Surface Wave (MASW) is one of the most
popular methods for Ground Roll (mainly Rayleigh wave) inversion
MASW is applied to different real data sets from La Marque Geophysical
Observatory, TX
Effect of a Near-surface Low-velocity Layer in x-t domain data
-Dulaijan, 2008 (modified after Farrell et al., 1984)

4. MASW in Nutshell - Xia et al., 1998 - Park et al., 1998 F.T.
Shot gather
- Xia et al., 1998
- Park et al., 1998

5. La Marque Geophysical Observatory University of Houston Coastal Center
Galveston County, Texas N
Sledgehammer-
Planted Geophone
Entrance
Sledgehammer-
Land Streamer
Accelerated Weight Drop-
Planted Geophone
UH Coastal Center
Galveston, Texas

6. La Marque Geophysical Observatory
The topography of the field site is flat.
Sediments are from the Quaternary Beaumont Formation
consisting of clay and silty clay (Capuano et al., 1996).
One seismic experiment was performed along the road whereas
other two was done on solid land blocks
Seismic Experiments
Experiment 1:
Source: 10 lb Sledgehammer Receiver: Land Streamer
Experiment 2:
Source: 10 lb Sledgehammer Receiver: Planted Geophone
Experiment 3:
Source: Accelerated Weight Drop Receiver: Planted Geophone

7. La Marque Geophysical Observatory
Sledgehammer-Planted Geophone
Sledgehammer-Land Streamer N W E
Sample Interval: 0.5 ms
Record Length: 2 sec S
Sample Interval: 2 ms
Record Length: 3 sec

8. La Marque Geophysical Observatory
Accelerated Weight Drop – Planted Geophone W E
Sample Interval: 0.5 ms
Record Length: 3 sec

9. Raw Shot Gathers Sledgehammer- Land Streamer Sledgehammer-
Planted Geophone
OBSERVATION #1 : Raw Shot Gather Quality Is
Better for Planted Geophone Cases
Accelerated Weight
Drop–Planted Geophone

10. Dispersion Curves: Sledgehammer-Land Streamer
Near-field effects :
Non-stabilized surface waves
Degrade near-offset lower frequencies (having deeper
information) in the fundamental mode.
Far-field effect:
Dominance of higher modes
Affect the higher frequencies (having shallower
information) of the fundamental mode
λ≈ 20m
DMax ≈ 10m
OBSERVATION#2:
Depth Penetration ≈ 10m

11. Higher Modes Dispersion Curves: Sledgehammer-Planted Geophone
OBSERVATION#3:
Better Mode Separation
Lower Noise Level
Depth Penetration ≈ 22.5m
Higher Modes
λ≈ 45m
DMax ≈ 22.5m

12. Dispersion Curves: Accelerated Weight Drop – Planted Geophone
λ≈ 36m
DMax ≈ 18m
OBSERVATION#4:
Depth Penetration ≈ 18m

13. 2-D Shear-wave Velocity Profile
Sledgehammer-Land Streamer
Observation#5:
Road
Sledgehammer-
Land Streamer
tStatics = ∑ Δzi / Vi
Sledgehammer-Planted Geophone
Sledgehammer-
Planted Geophone

14. Is There Any Shear Wave Anisotropy ?
1026
1025
1023
1022
1026
1025
1023
1022

15. Future Plans Use of higher modes Passive MASW
Synthetic modeling using Finite-Difference code
Well log and VSP at La Marque Geophysical Observatory
Comparing MASW statics with regular statics

16. Acknowledgement Dr. Robert R. Stewart Dr. C. Liner
AGL colleagues- Ms Tania Mukherjee, Mr. Bode Omoboya, Mr. Anoop William
Mr. Li Chang and Mr. Joe Jackson