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Introduction to Geophysics Ali Oncel [email_address] Department of Earth Sciences KFUPM Refraction Seismology: Field Work Introduction to Geophysics-KFUPM
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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
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Types of Refraction Seismometer Introduction to Geophysics-KFUPM Geometrics StrataView OYO Geospace DAS 1
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Refraction Survey Introduction to Geophysics-KFUPM
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Geophone spread for a refraction survey with shot locations indicated Introduction to Geophysics-KFUPM
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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 ?
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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
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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
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Introduction to Geophysics-KFUPM Refraction Profile 2m
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Pick First Arrivals Example: Santa Teresa Hills Introduction to Geophysics-KFUPM
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Example: Santa Teresa Hills You can plot the measured data under EXCELL and show the data in this way. Introduction to Geophysics-KFUPM
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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
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Example: Forward and Reversed Introduction to Geophysics-KFUPM We have just made Forward, so you can ignore the Reversed
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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
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Both on Same Plot Introduction to Geophysics-KFUPM
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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
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Generate Data Table Introduction to Geophysics-KFUPM
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Example: Interpreted Plot Introduction to Geophysics-KFUPM Include T intercepts and crossover distances
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Determine slopes and intercept values Introduction to Geophysics-KFUPM
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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.
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Field Study Report Format, Due March 18 <ul><li>Statement of Geologic Problem (1/2 page) </li></ul><ul><li>Theoretical Background (1-2 pages with 2-3 diagrams) </li></ul><ul><li>Data Acquisition (1-2 pages, 1-2 diagrams) </li></ul><ul><li>Data Processing (1-2 pages, 1 diagram - processing flow) </li></ul><ul><li>Interpretation (1 page, 1 diagram - model) </li></ul><ul><li>Conclusions (1/2 page) </li></ul><ul><li>References (3 or more citations) </li></ul>Introduction to Geophysics-KFUPM
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