The time variation of crustal velocities in tectonic regions is most reasonably attributed to stressinduced variations in crack porosity. The decrease in V•,/Vs before arthquakes is due primarily to a large decrease in Vp. This supports the Nur dilatancy hypothesis but not the effective stress hypothesis. New data from the San Fernando region verify the Vp drop, show that this drop cannot be en...

Seismologists, like mathematicians, are accustomed to dividing their subject into a pure and an applied branch. The desirability of such division is underlined by the manner in which non-seismologists frequently approach the subject. I t is too often taken for granted that, because an earthquake is a motion of the ground, seismology must be chiefly concerned with the detailed analysis of that m...

range and the location of artificial reflectors or intermediate values at these points. A similar fictitious sources inherent in discrete wave economy can be obtained using the itrerative reflection and transmission coefficient relations number techniques. The number and spacing of wave numbers in wave number integration schemes are of Kennett. Kamel and Felsen (1981) presented a hybrid determi...

In this chapter, we summarize and synthesize our investigations of the use of evolutionary algorithms to automatically program robots, particularly for application to space exploration. In the Space Robotics Group at the University of Toronto Institute for Aerospace Studies, we were motivated to begin work in this area a decade ago when the concept of network science became popular in the space...

Imaging the interior of a region with waveforms recorded on the surface is a key application of scattering theory in geophysics, medical imaging and many other fields. In this chapter I will discuss how the waveform inversion problem can be formulated in terms of statistical inference. Statistical methods are essential in order to be able to take into account the limited, uncertain nature of th...

The history of seismology has been traced since man first reacted literarily to the phenomena of earthquakes and volcanoes, some 4000 yr ago. Twentysix centuries ago man began the quest for natural causes of earthquakes. The dawn of modern seismology broke immediately after the Lisbon earthquake of 1755 with the pioneering studies of John Bevis (1757) and John Miehell (1761). It reached its pin...

Not too long ago, seismic imaging of the Earth’s interior relied almost exclusively on the illumination from energetic sources, such as earthquakes or artificial sources. However, recent theoretical and laboratory studies have shown that the impulse response (Green’s function) of a structure between two receivers can be obtained from the cross-correlation of “random” noise wavefields recorded a...

Converted and multiply reflected phases from teleseismic events are routinely used to create structural images of the crust-mantle boundary (Moho) and the elasticity contrasts within the crust and upper mantle. The accuracy of these images is to a large extent determined by the background velocity model used to propagate these phases to depth. In order to improve estimates of 3-D velocity varia...