The Mechanics of Earthquakes and Faulting: (C. H. Scholz)

Abstract

Have you wondered why those short, en echelon, calcite-filled fractures that all geologists have seen have a mild “S” shape? Why are the en echelon fractures oriented at an angle to the trend of the fracture zone? Which came first, the fault or the shear zone? Why are map traces of strike-slip faults straighter than dip-slip faults? How are tension cracks and shear cracks related? Why are fault-bend folds more pronounced on thrust faults than on other fault types? The answers to these and other questions can be found in Christopher Scholz's 2003 book The Mechanics of Earthquakes and Faulting , published by Cambridge University Press. The second edition of 2002 was reprinted with corrections in 2003. This upper-division/graduate level reference book is organized into seven chapters. Chapter 1 addresses brittle fracture of rock, including pore-fluid effects on fracture and brittle-plastic transitions caused by pressure and temperature, and extrapolates laboratory results to geological conditions. The three modes of crack propagation from fracture mechanics are described early in the chapter. These modes should be understood by all geologist working on ground-deformation problems, including landslides and subsidence, where distribution and nature of cracks is fundamental to interpretation of process. Rock friction, the subject of Chapter 2, is a contact property of faults that already exist; it is not a bulk property. This chapter sets the stage for an understanding that seismic or aseismic fault motion is governed by the stability of friction. Fault surfaces have topography and touch only at asperities. Asperity area increases as shearing occurs, but other aspects of interaction contribute to actual friction: ploughing, riding up, and interlocking. Regular stick slip is dynamic instability with all sliding during the instability. A mechanism proposed for earthquakes is recurring slip instability on pre-existing faults that remain stationary between earthquakes. Unstable sliding …