Seismic Waves and Seismographs

Physics of Waves

Wave Simulations Colorado School of Mines Tutorial Colorado School of Mines Tutorial Wave Basics

LL F L F = k *  L/L (Hooke’s Law) k = Young’s modulus Stress = F/A = K  u/  x= Strain Rand quartzite strain Elastic Materials

Elastic Waves Force = Mass x Acceleration (Newton rules!) u u+ du x x + dx A F(x) F (x+dx) Net force = F(x+dx) – F(x) =  F = [  *Area*dx] *acceleration  F/  x =  * acceleration * Area] but F = Stress/Area = K *  u/  x (Hookes law) so K *  u/  x  x = K  u 2 /  x 2 =  *  u 2 /  t 2 i.e. a wave equation where V= (k  ) 1/2

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

Seismic Waves

Seismic Waves Body Surface P S Love Rayleigh

Surface (Rayleigh) Waves

Seismic Wave Speeds MaterialP wave Velocity (m/s)S wave Velocity (m/s) Air332 Water Petroleum Steel Concrete Granite Basalt Sandstone Limestone Sand (Unsaturated) Sand (Saturated) Clay Glacial Till (Saturated)

P vs S

Seismometry earthquake.usgs.gov/4kids/games/ coloring/seismograph.gif geology/geo101/quakelec.htm

Pendulum Seismograph science/seismograph.GIF T= 2  L/g For T= 1 sec, L =.2 m T= 20 sec, L = 99 m

Seismograph Response

Seismograph Response Curve man_html/node10.html

Dispersion Kanamori and Abe (1968) Fig Stein and Wysession (2003) Oliver (1962) Love Waves

Vertical Seismograph Bolt, 1993

Horizontal Seismograph (Swinging gate) library.thinkquest.org/ 15616/aard4n.html

Seismic Station

Seismic Pier Remote Display

Seismometer/graph Menagerie