This essential reference for graduate students and researchers provides a unified treatment of earthquakes and faulting as two aspects of brittle tectonics at different timescales. The intimate connection between the two is manifested in their scaling laws and populations, which evolve from fracture growth and interactions between fractures. The connection between faults and the seismicity generated is governed by the rate and state dependent friction laws - producing distinctive seismic styles of faulting and a gamut of earthquake phenomena including aftershocks, afterslip, earthquake triggering, and slow slip events. The third edition of this classic treatise presents a wealth of new topics and new observations. These include slow earthquake phenomena; friction of phyllosilicates, and at high sliding velocities; fault structures; relative roles of strong and seismogenic versus weak and creeping faults; dynamic triggering of earthquakes; oceanic earthquakes; megathrust earthquakes in subduction zones; deep earthquakes; and new observations of earthquake precursory phenomena.

The Mechanics of Earthquakes and Faulting

Stress corrosion cracking of six glasses was studied using fracture mechanics techniques. Crack velocities in water were measured as a function of applied stress intensity factor and temperature, and apparent activation energies for crack motion were obtained. Data were consistent with the universal fatigue curve for static fatigue of glass, which depended on glass composition. Of the glasses tested, silica glass was most resistant to static fatigue, followed by the low-alkali aluminosilicate and borosilicate glasses. Sodium was detrimental to stress corrosion resistance. The crack velocity data could be explained by the Charles and Hillig theory of stress corrosion. It is probable that stress corrosion of glass is normally caused and controlled by a chemical reaction between the glass and water.

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Stress Corrosion and Static Fatigue of Glass

Fracture surface energies of six glasses were measured using the double-cantilever cleavage technique. Values ranged from 3.5 to 5.3 J/m2 depending on the chemical composition of the glass and the temperature of the test. The fracture surface energy increased with decreasing temperature and increasing Young's modulus; however, exceptions to this behavior were noted. The magnitude of the values obtained is discussed with respect to the theoretical strength of glass and possible irreversible effects at the crack tip such as stress corrosion and plastic deformation are considered.

Fracture Surface Energy of Glass

Nearly 200 samples of single-crystal quartz were broken in uniaxial compression. The quartz was observed to exhibit strong static fatigue, the mean fracture time 〈t〉 being related to stress σ, concentration of water CH,O, and temperature T by 〈t〉 = t0 CH2O−;α exp [(u′/RT) − κ′σ]. Microfracturing associated with crack growth and spalling occurred continuously during the experiments. No creep strains could be detected. The rate of microfracturing n followed the expression n = a0 CH2O α exp [(−u′/RT) + κ′σ]tγ. These and other results suggest that static fatigue of quartz is due to stress corrosion cracking. The most likely mechanism is a silica hydration reaction. Static fatigue is suggested as the mechanism of brittle creep of rocks and of time-dependent earthquake phenomena.

Static fatigue of quartz

After a brief review of early lightguide work, the authors assess advances since the mid-1970s. They note important work on strength distributions and procedures for improving strength. This is followed by a discussion of long-length strength, prooftesting and splicing. Flaw character is studied along with strength degradation, fatigue limits, aging and fatigue, and hermetic coatings. >

Strength and fatigue of silica optical fibers

Silica fibres and flame polished rods having strengths around 600 Kg/mm2 were prepared and the preparation conditions studied. The effects on fibre strengths of atmospheric and temperature changes, and of variations in rate of stressing and previous heat treatment, were extensively investigated. From the results obtained a comprehensive qualitative picture of the strength of silica has been deduced; it is found to be strongly dependent on the testing conditions and to extend over the range 280 to 1500 Kg/mm2. INTRODUCTION With the increasing interest in composite materials, in which the load is borne by fibres of a brittle material, it becomes more and more important to understand the factors which govern the strength of brittle materials. This work on fused silica formed part of a more general study of composites and the context was briefly described by Morley (i964). The strength of silicate glasses has been studied for many years but until quite recently all work was carried out with 'weak' specimens which had suffered abrasive surface damage in their preparation or testing. Since the importance of surface damage was scarcely recognized and handling techniques varied widely, this led to very variable strengths, irreproducibility of results from one laboratory to another and a large apparent size dependence of strength. Further, true variations in the strength of the material (due to temperature, moisture, etc.) were often obscured or confused by the effects these variables had on the nature of the existing surface flaws. In this work high strength silica samples were prepared by adapting and extending the techniques of fibre production and handling described by Morley, Andrews & Whitney (i964). Stringent precautions were taken to avoid any contact whatso- ever with the surface of the silica under test and strengths up to 150OKg/mm2 were obtained under certain test conditions. It seems possible that the true strength of the material was being measured. These same high strength samples were studied under a wide range of conditions and the strength was seen to be a complex function of the atmosphere in which the silica was stressed, the temperature, and the rate of stressing. Specific damaging or weakening effects due to heat treatment or specimen preparation could be superimposed on the other factors. In attempting to present a clear account of the strength behaviour we describe each effect in a separate section of the paper. Some discussion of proposed mechan- isms has been introduced at each stage since this appeared necessary to explain the results described in following sections.

J. W. Johnson

Papers

The strength of fused silica