EXERSISE FOR SESMIC REFRACTION, Exercises of Geophysics

Download EXERSISE FOR SESMIC REFRACTION and more Exercises Geophysics in PDF only on Docsity! Seismic Refraction Assignment_WU 1. Construct a travel time curve to a distance of 120 m for a structure with an 10 m thick soil layer with P-wave velocity 500 m/s over a saturated layer 20 m thick with P-wave velocity 1500 im/s over bedrock with velocity 3000 m/s. From the graph, what are the 2 crossover distances? Does the first crossover distance value agree with what you calculate using the following equation? (6 points) TT “WV. =V, 2. Construct a travel time curve for the following data for both the forward and reverse profiles. Evaluate slopes and intercept times, and use those values to determine the subsurface structure for the first 2 layers, and then estimate (do not try to calculate!) the properties of the bottom layer. Offsets are in meters and times are in milliseconds. (8 points) Offset x 5 10 15 20 25 30 35 40 45 50 55 60 Forward 83 16.7 25.0 33.3 41.7 50.0 58.3 66.7 72.5 75.1 77.7 80.3 Reverse 83 10.7 25.0 33.3 40.7 443 48.0 51.6 55.3 58.9 62.6 066.3 3. The following data are from a profile over a buried steep fault scarp underlying alluvium. Use the data to determine velocities for the alluvium and bedrock and the throw and approximate position of the buried fault step. Offsets are in meters and times are in milliseconds. (8 points) Offset x 5 10 15 20 2 30 35 ©6440 45 50 55 60 Forward 36 71 10.7 143 17.9 214 23.0 24.0 24.9 25.8 26.7 27.7 Reverse 36 71 107 143 179 214 25.0 286 304 25.8 26.7 27.7 Offset x 65 70 75 80 8 90 95 100 105 110 115 120 Forward 28.6 295 304 314 358 36.7 37.7 386 395 404 414 423 Reverse 28.6 295 304 314 323 33.2 341 35.1 360 36.9 37.9 388 4. Apply the 'plus-minus' method to the set of data below. Offsets are in meters and times are in milliseconds. On graph paper, plot the travel time curves (forward and reverse), identify the paired refractions, and then apply the formulas in the text to determine ATp and hp, given the information V1 = 1500 m/s, V2 = 4000 m/s, and reciprocal time Tt = 25.8 milliseconds. Offset(m) 5 10 15 20 25 30 35 40 45 50 55 60 tsp (ms) 3.3 67 100 133 167 194 203 212 221 23.0 240 24.9 tsp (ms) 3.3 607 100 117 #133 148 164 #180 195 211 227 242 Finally, make a plot of tsp - ts'D versus offset x and use the value of the slope to confirm the value of V2. (8 points). By Geremew Lamessa(PhD)