This record summarises seismicity induced by hydrofracturing. It begins with a list of issues of concern to the public about hydrofracturing.
The types of fracturing are then defined-tension, shear and hybrid tension and shear-and a failure mode diagram that explains the fluid pressure and stress regimes under which each is likely to occur is introduced. The report sets out the conditions under which fresh rock is fractured and pre-existing weak faults are reactivated. Fractures grow by small increments, with each increment causing a small earthquake. Earthquake magnitudes and intensities are explained so that the fracture size can be related to earthquake magnitude. What people feel is explained in terms of earthquake intensity. The size distribution of earthquakes induced by hydrofracturing of both intact rock and reactivating existing weak faults is then summarised based on case studies in the scientific literature.
The background established in the first part of the record is then applied to hydrofracturing in the coal seam gas, shale gas, enhanced geothermal and carbon sequestration sectors. The record concludes by explaining how hydrofracturing and induced seismicity contribute to a discussion of the issues of public concern listed in the introduction to the record.
The record is in two parts-the main body of the record and four appendices. The main body is written in a form readable to non-seismologists, although a basic understanding of the scientific principles considered in the record would be an advantage. A more theoretical treatment of the hydrofracture process and earthquake size is given in the first two appendices. The third appendix discusses larger induced earthquakes attributed to a number of causes, including the reinjection of waste water from the unconventional gas industry. The fourth appendix summarises the current approaches to the regulation of the hydrofracturing process in several jurisdictions in Australia.
