Earthquakes are due to the fast propagation of shear faults in the earth. They occur on active fault systems after a long and complex process of stress accumulation over various time and spatial scales. In this course we will address the problem of shear fracture in the earth under the control of friction, butthe main emphasis will be on the generation of seismic waves and strong ground motion. Slow slip on fault zones, an integral part of the process that leads to sudden earthquake rupture, will also be discussed with reference to large subduction zones.
Topics that will be addressed include fault friction, macroscopic failure criteria, effective stress laws, rheology and a detailed description of the theory of rupture nucleation and propagation. We will study in detail the circular fault model used by seismologists to understand the classic scaling laws of seismic radiation at low frequencies. The origin of seismic moment, seismic energy and the scaling between these and other physical parameters will be studied in detail. The origin of higher frequencies, beyond the corner frequencies is still a difficult research subject, we will review the different theories, both kinematic (k-squared) and dynamic (effects of rupture velocity changes including super-shear pulses and stress heterogeneity).
We will extensively use modern digital accelerograms to compute source parameters including seismic moment, radiated energy, spectral properties, earthquake size, friction laws and strong ground motion parameters. The main events we will use are from Japan (strike slip) and Chile (subduction zone).