William B. Joyner Memorial Lectures

Abstract

Charles Lyell (1797–1875) was the great advocate of “Huttonian” principles, whereby present Earth activity is regarded as the key to interpreting past rock assemblages. His famous Principles of Geology went through twelve editions between 1830 and 1876, over which time his thoughts on the relationship between earthquakes and faults evolved considerably. The first edition was Charles Darwin's vade mecum on the voyage of the Beagle (1832–1836), constantly referred to (Darwin, 1845). In the course of this voyage Darwin observed more than 3 m of coastal uplift accompanying the great Chilean earthquake of 1835. Few seismologists today would consider anything other than gigantic shear rupture as the cause of this and other subduction earthquakes, despite the fact that they occur offshore along unseen subduction thrust interfaces. In fact, our belief that a large earthquake requires shearing along a large fault rupture can be traced back to observations of fault rupture accompanying the 1855 Wairarapa earthquake in New Zealand, subsequently reported in the 10th edition of Principles of Physical Geology (1868), where Lyell pronounced: The geologist has rarely enjoyed so good an opportunity as that afforded him by this convulsion in New Zealand, of observing one of the steps by which those great displacements of the rocks called `faults' may in the course of ages be brought about. My purpose here is to draw together some of the historical threads that led Charles Lyell to make this pronouncement on the relationship between earthquakes and fault rupture, which represented a significant advance in our understanding of earthquake source mechanics. The history of ideas on earthquakes and their cause is vast (see extensive discussion on the HEAT Web site; Oeser, 2005). My selection may be criticized as overly anglocentric, but I have sought the roots of the ideas that would have influenced the evolution …