The document discusses refraction seismology field work. It covers types of seismometers used, how a refraction survey is set up with geophone spreads and shot locations, and controlled seismic sources like impact and vibrating sources. An example refraction profile from Santa Teresa Hills is shown and discussed, including determining intercept times and velocities to develop a geophysical model of subsurface layers. Students are assigned a field study report on their refraction data due next month.

1. Introduction to Geophysics Ali Oncel [email_address] Department of Earth Sciences KFUPM Refraction Seismology: Field Work Introduction to Geophysics-KFUPM

2. Previous Lecture Earthquake Waves: As Probes of Earth's Interior Travel Time Models of Earthquakes for flat earth Travel Time Models of Earthquakes for Curved earth Field Work: Refraction Introduction to Geophysics-KFUPM

3. Types of Refraction Seismometer Introduction to Geophysics-KFUPM Geometrics StrataView OYO Geospace DAS 1

4. Refraction Survey Introduction to Geophysics-KFUPM

5. Geophone spread for a refraction survey with shot locations indicated Introduction to Geophysics-KFUPM

6. What does gravity surveying or “gravity” measure? Variation in gravitational acceleration ? km ? km Shot #1 Shot #2 Bedrock = V 2 = xxxx ft/sec Alluvium = V 1 = xxxx ft/sec x km Corrected Dip =? o Ground slope = x o Develop a Geophysical Model We made a single shot and ignored the reversed one? What is the significant of reverse shot through the developing geophysical model? Introduction to Geophysics-KFUPM ?

7. Determine slopes and intercept values You should have already had experience in estimating required parameters which are needed for geophysical model. What about your homework? Deadline is already finished! Introduction to Geophysics-KFUPM

8. Controlled Seismic Sources Impact Sources Vibrating Explosive Sources Seismic waves are generated using a number of different source types: • weight-drop sources (e.g. hammer strike on steel plate) • accelerated weight drop • vibrating sources (‘vibroseis’) • explosives (dynamite, downhole shotgun) Introduction to Geophysics-KFUPM

9. Introduction to Geophysics-KFUPM Refraction Profile 2m

10. Generating Seismic Source Introduction to Geophysics-KFUPM Shot 1 Shot 1

11. Introduction to Geophysics-KFUPM

12. Pick First Arrivals Example: Santa Teresa Hills Introduction to Geophysics-KFUPM

13. Example: Santa Teresa Hills You can plot the measured data under EXCELL and show the data in this way. Introduction to Geophysics-KFUPM

14. Example: Santa Teresa Hills What is the geophone distance in this example? 30 m What was the geophone distance considered in our work? 3 m What makes differences between geophones? Introduction to Geophysics-KFUPM

15. Example: Forward and Reversed Introduction to Geophysics-KFUPM We have just made Forward, so you can ignore the Reversed

16. Example: Santa Teresa Hills What is the geophone distance in this example? 30 m What was the geophone distance considered in our work? 3 m What makes differences between geophones? Introduction to Geophysics-KFUPM

17. Both on Same Plot Introduction to Geophysics-KFUPM

18. Example: Santa Teresa Hills What is the geophone distance in this example? 30 m What was the geophone distance considered in our work? 3 m What makes differences between geophones? Introduction to Geophysics-KFUPM

19. Generate Data Table Introduction to Geophysics-KFUPM

20. Example: Interpreted Plot Introduction to Geophysics-KFUPM Include T intercepts and crossover distances

21. Determine slopes and intercept values Introduction to Geophysics-KFUPM

22. Introduction to Geophysics-KFUPM Your Model for Flat Layer Your model is very simple since we forward shot and assumed the surfaced layer which is flat. Thus, you are asked to estimate velocities and thickness. Use the data you measured in the to calculate unknown variables.