Structural geology

I have measured structures in the field and from images for many years. My focus has been on brittle tectonics, particularly joints, tension fractures, strike-slip and normal faults, veins, dykes, inclined sheets, sills, collapse calderas, and plutons. In addition, I have a long experience in analytical and numerical modelling of field structures. In particular, I have measured veins, tension fractures, and faults in the field and calculated the driving stresses associated with their displacements (openings, throws, vein and dyke thicknesses) using analytical (fracture mechanics) methods. My students and I have also made many numerical models of fault linkage, the evolution of sets of tension fractures and faults (fissure swarms), and the interaction between large fault zones and nearby volcanoes. These techniques and many solved problems (worked examples) are presented in detail in Rock Fractures in Geological Processes (cited) and in some of the figures presented here.

Recently, I began to use thermodynamics/statistical mechanics principles to fracture populations, in particular to fissure swarms, fault zones, and rift-zone segments. My colleagues and I calculate the  power-law scaling exponents and the  (Gibbs/Shannon) entropies of tectonic fractures, ranging in length by five orders of magnitude, from four networks at the plate boundary in Iceland. Each network can be divided into populations based on abrupt changes (breaks) in the scaling exponents. The breaks, we suggest, are related to the comparatively long and deep fractures changing from tension fractures to normal faults and penetrating the contacts between the Holocene lava flows and the underlying and mechanically different Quaternary rocks.

The results show a strong linear correlation between the population scaling exponents, the fracture length ranges and average lengths, and the calculated entropies. The correlation is partly explained by the entropy (and the scaling exponent) varying positively with the length range (the difference between the longest and the shortest fracture) of the populations in each network. Currently, I am working on how to relate the calculated entropies to the thermodynamic principles that control fracture initiation and propagation (the theory of Griffith). We have applied the same method to analysing other lineament patterns, such as streets in cities of various shapes and sizes.

Selected publications on this topic

Gudmundsson, A. and Brenner, S.L., 2003.
Loading of a seismic zone to failure deforms nearby volcanoes: a new earthquake precursor.
Terra Nova 15, 187 – 193.

Mohajeri, N., Gudmundsson, A., 2012.                                                                     Entropies and scaling exponents of street and fracture networks.                               Entropy (in press).

Gudmundsson, A. 2011.                                                                                                   Rock Fractures in Geological Processes.                                                                 Cambridge University Press.

Gudmundsson, A., Mohajeri, N., 2011.                                                              Thermodynamic aspects of the development of fracture networks.                                 Bull. Geol. Soc. France (submitted).