Lecture 11 13 2 Source Effects 1 Location proximity Closer you are to the eq stronger the ground shaking motions 2 Magnitude Larger the eq is larger the magnitude more ground motions 3 Duration Fault is unzipping at Propagation velocity 3km s 1906 eq started right next to San Francisco took 100s 2mins to get to the north end Time period generating energy is 2 mins 4 Frequency content of seismic waves Everything has a natural harmonic frequency at which it vibrates resonance Big things low frequency small things high frequency Shear waves in the crust move almost as fast as the rupture front Shear waves propagate at about 80 as fast as rupture waves 5 Rupture directivity Rupture propagation direction fault slip direction Don t no source directivity Beyond 10km
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