TAG 166 - Geological Society of Australia

Book ReviewsGeology of the EarthquakeSourceA volume in Honour of Rick SibsonÅ Fagereng, VJ Toy and JV Rowland (Eds)Geological Society of London, SpecialPublication 359, London 2011, 341 pages.ISBN 978-1-86239-337-0This Special Publication of the GeologicalSociety is a well-presented compilation ofpapers, some of which were given at a specialsymposium Geological and GeophysicalSignatures of Earth Deformation and FluidFlow held at Oamaru, New Zealand inNovember 2009.It surprised me to see that of the 18 papers,Sibson was the author of one paper and jointauthor of another in a volume dedicated tohonouring him, his research-inspired teachingrole and his efforts to integrate structuralgeology and seismology. The editors havegrouped the papers into broad headings:Observations in active fault zones; Fault rocksand fault-slip styles; The base of theseismogenic zone; Effects of fluids onfaulting; and Fault reactivation vs initiation.The sections are book-ended with a veryuseful introduction by the first two namededitors, and Future directions, ‘The scope ofearthquake geology’, from Sibson himself.Thankfully the editors included an index.The earthquake source zones sampled includeItaly, Japan, the Middle East, New Zealand,Norway, Turkey, Taiwan, the USA andsurprisingly Australia — one of them justdown the road from my office and over theborder at Taemus, NSW.It is a pity there are such lean pickings forseismologists in the book although it stillshould be on every Earth Scientist’s readinglist, seismologists included, thanks to Sibson’slast chapter. Mostly the authors have focusedon interpreting ancient rock deformationstructures without the benefit of comparingthem with the deformation observable inrecent earthquakes where the fault skylightsor ruptures deep mine leads. The educationalprocess should work both ways. Toy, Ritchieand Sibson discuss the brittle–ductiletransition zone at the central Alpine Fault inNew Zealand without discussing why theearthquakes occur within the hangingwalland not on the fault itself. Neither do theydiscuss why the transition zone is so shallowat 8.5 km, whereas earthquakes occur todouble that depth in Eastern Australia wherethe basement rocks are of similar age. Thisobservation of current small earthquakesbeing restricted within the hangingwall andnot on the fault has been made on theLapstone Fault in eastern NSW (Gary Gibson,pers. comm., 2005).Whether earthquakes create new faults orre-rupture existing faults has often been amatter of dispute between seismologists(see Sibson’s last chapter). However, Nortjeand others in their analysis present tangibleevidence for both mechanisms in their studyof copper mineralisation at Mount Isa. Scholzalso addresses this issue briefly, explainingwhy splay faults can be so important inthe process of reactivation of seeminglyunfavourably oriented faults.The final chapter by Sibson is a good read,covering the 40-odd-year history of earthquakegeology. He points to the need forbetter definition of fault zone models: theChristchurch earthquakes and large intraplateareas such as Australia are good examples ofsuch a need. He points out that earthquakesdo occur in what would normally be regardedas the ductile zone right down to the mantle.In passing, he states that the recurrenceintervals on ‘active’ faults within intraplateareas may approach 10 000 years or more.Sibson also suggests that research relatinggeological (ie, paleoseismological)observations to the physics of earthquakerupturing would be fruitful (are earthquakesfluid-driven or stress-driven?), that dynamictriggering of small earthquakes by distantgreat earthquakes is a reality (pooh-poohedby some Australian seismologists), and thereis a need to develop sampling and statisticaltechniques to positively identify majorearthquakes in the geological record.I seem to remember John Tchalenkoencouraging the Imperial College earthquakeengineering students to attend one of Rick’stalks in the very early 1970s and I wish I hadhad the time to listen to more of them.Undoubtedly seismologists need to learnmore from geologists to refine their modelsand vice versa. Both need to learn more aboutthe physics of the earthquake source.The more I read this book, the more I warmedto it. Good thoughtful source material for allearthquake geologists and seismologists.KEVIN McCUEUniversity of Central QueenslandPalaeoproterozoic of IndiaR Mazumder and D Saha (Eds)Geological Society of London, SpecialPublication 365, London 2012, 290 pages.ISBN 978-1-86239-345-5The editors have pulled together 13 papers toproduce another quality Geological SocietySpecial Publication. The book emanates froma conference and post-conference fieldworkshop related to the UNESCO-IGP 509project on Palaeoproterozoic Supercontinentsand Global Evolution.The Indian shield comprises a number ofmajor and minor Paleoproterozoicsedimentary basins and supracrustalsequences developed on four large Archeannuclei. The papers in this volume coveraspects of regional geology and have allowedthe various authors to put portions of theIndian subcontinent into a global context.This is a particularly important outcome giventhe size of India. Furthermore it adds a substrateto country-scale evaluation for mineralexploration in a country that undoubtedlyhosts major undiscovered mineral deposits.The Paleozoic era spans the period ofca 2500–1600 Ma and has been interpretedby some authors as the first supercontinentcycle. Importantly, it encompasses one ormore global tectonic events and implicatesprocesses associated with the core, mantle,lithosphere, hydrosphere, atmosphere andbiosphere. As such, the volume is a welcomecontribution to the overall understanding ofthis period.TAG March 2013| 43