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ÖNCEL AKADEMİ: INTRODUCTION TO GEOPHYSICS
1. Introduction to Geophysics Ali Oncel [email_address] Department of Earth Sciences KFUPM Seismic Reflection 4: Acquisiton, Processing, and Waveform Analysis Introduction to Geophysics-KFUPM
2. Types of Velocities Average Velocity Root mean Square Velocity (RMS) Interval velocity Previous Lecture Introduction to Geophysics-KFUPM
3. Example: Disk Formula v 1 =1500 m s -1 v 2 =2000 m s -1 v 3 =2345 m s -1 t 1 =2.14 s t 2 =1.21 s t 3 =1.13 s What is v rms at the base of layer 3? Introduction to Geophysics-KFUPM
7. “ 12 elephants dancing in unison” (LITHOPROBE, CANADA) A vibrator truck Vibroseis images from the Lithoprobe Project, Canada www.lithoprobe.ca Introduction to Geophysics-KFUPM
11. Example: Air-water reflection ρ air =0; Vp=330 m/s ρ water =1; Vp=1500m/s R AirWater = (I Water -I Air ) / (I Air +I Water ) R AirWater = (I Water -0) / (0+I Water ) R AirWater = 1 Introduction to Geophysics-KFUPM Air Layer 1 Layer 2
12. ρ air =0; Vp=330 m/s ρ water =1; Vp=1500m/s Example: Water-air reflection R WaterAir = (I Air -I Water ) / (I Air +I Water ) R WaterAir = -1 ( A negative reflection coefficient) Introduction to Geophysics-KFUPM Air Water Layer 1 Layer 2
15. Introduction to Geophysics-KFUPM b) Seismic response for reflection at interface with positive reflection coefficient c) Seismic response for negative reflection coefficient Fig. 5.26 of Lillie a) Input minimum phase and zero phase seismic signals
Whether the reflected wave has the same or opposite polarity as the input seismic signal depends on whether the reflection coefficient is positive or negative.
Convolution means replacing each reflection coefficient with the input seismic signal, scaled to the amplitude and polarity of the reflection coefficient.