Seismic Waves and Seismographs Physics of Waves Wave

Seismic Waves and Seismographs

Physics of Waves

Wave Simulations Colorado School of Mines Tutorial Wave Basics

Elastic Materials L strain F DL F = k * DL/L strain Rand quartzite (Hooke’s Law) k = Young’s modulus Stress = F/A = K Du/Dx= Strain

Elastic Waves Force = Mass x Acceleration (Newton rules!) F(x) F (x+dx) A x x + dx u u+ du Net force = F(x+dx) – F(x) = DF = [r *Area*dx] *acceleration DF/Dx = [r * acceleration * Area] but F = Stress/Area = K *Du/Dx (Hookes law) so K * D(Du/Dx)Dx = K Du 2/Dx 2 = r * Du 2/Dt 2 i. e. a wave equation where V= (k/r)1/2

Seismic Wave Equation d 2 u/dx 2 = (r/k) du 2/dt 2 which has solutions of the form U(x, t) = A e-i(kx-wt) + Be-i(k+wt)

Seismic Waves http: //www. uwgb. edu/dutchs/Earth. SC 202 Notes/quakes. htm

Seismic Waves P Body S Love Surface Rayleigh

Surface (Rayleigh) Waves

Seismic Wave Speeds Material P wave Velocity (m/s) S wave Velocity (m/s) Air 332 Water 1400 -1500 Petroleum 1300 -1400 Steel 6100 3500 Concrete 3600 2000 Granite 5500 -5900 2800 -3000 Basalt 6400 3200 Sandstone 1400 -4300 700 -2800 Limestone 5900 -6100 2800 -3000 Sand (Unsaturated) 200 -1000 80 -400 Sand (Saturated) 800 -2200 320 -880 Clay 1000 -2500 400 -1000 Glacial Till (Saturated) 1500 -2500 600 -1000

P vs S

Seismometry earthquake. usgs. gov/4 kids/games/ coloring/seismograph. gif www. gpc. peachnet. edu/~pgore/ geology/geo 101/quakelec. htm

Pendulum Seismograph T= 2 p L/g For T= 1 sec, L =. 2 m T= 20 sec, L = 99 m www. psd. wednet. edu/jrsrhigh/ science/seismograph. GIF

Seismograph Response http: //www. uwgb. edu/dutchs/Earth. SC 202 Notes/quakes. htm

Seismograph Response Curve www. geophys. uni-stuttgart. de/. . . / man_html/node 10. html

Dispersion Love Waves Kanamori and Abe (1968) Fig. 2. 8 -4 Stein and Wysession (2003) Oliver (1962)

Vertical Seismograph Bolt, 1993

Horizontal Seismograph (Swinging gate) library. thinkquest. org/ 15616/aard 4 n. html

Seismic Station

Seismic Pier Remote Display

Seismometer/graph Menagerie