Abstract - Movement of tectonic plates over the earth’s surface is responsible for deformation of the earth’s crust and the generation of fault systems covering large regions. Much of offshore Ireland and the North Sea owe their existence to ancient fault systems that are a response to extension of the earth’s crust and accommodate crustal thinning and subsidence with the formation of sedimentary basins. Until recently the structure and growth of such basins was relatively poorly defined. The acquisition of seismic reflection data has, however, provided high quality definition of the three-dimensional structure of basins down to depths of in excess of 10km. These data provide answers to a variety of fundamental questions about the growth of fault systems, and related earthquake characteristics, that cannot be established from other better known systems, such as the San Andreas fault system.
Fault systems are shown to comprise a population of interacting faults with a broad range of fault size, i.e. length or displacement. Large faults become large because they live longer and move faster than smaller faults. The preferential growth of large faults reflects the progressive localisation of displacement, and deformation, onto fewer and larger faults, a fundamental characteristic of fault systems on all scales. This progressive localisation is responsible for changes in the populations of earthquakes as a fault system matures. The existence of long range interactions between faults suggests that earthquakes on individual faults cannot be accurately predicted from historical earthquake data.
Royal Dublin Society, Occasional Papers in Irish Science and Technology,
21, John Jackson Lecture 2000, 16pp.