Peleg Wadsworth

The article reviews the life of Peleg Wadsworth, with particular emphasis on his role in the American Revolution

The structure and composition of exhumed faults, and their implications for seismic processes

Field studies of faults exhumed from seismogenic depths provide useful data to constrain seismologic models of fault zone processes and properties. Data collected on the San Andreas Fault in the San Gabriel Mountains has shown that large-displacement faults consist of one to several very narrow slip zones embedded in a cataclastically deformed sheared region several meters thick. However these faults have not been buried to depths greater than 5 km. Fault zones in the Sierra Nevada, California allow us to study the microstructures resulting from the deformation mechanisms active at seismogenic depths. Syn-fault mineralization shows that these left-lateral strike-slip faults formed at 5-12 km depth. Detailed microstructural analyses of the small faults reveal that they evolved from cooling joints filled by chlorite, epidote and quartz. These joints were then reactivated to form shear faults with accompanying brittle fracture and cataclastic deformation, ultimately developing very fined-grained cataclasites and ultracataclasites. The shear-induced microstructures are developed on faults with as little as several mm of slip showing that narrow slip-surfaces develop early in the lifetime of these faults. Subsequent slip has little effect on the microstructures. The inferred similarity of deformation mechanisms in faults 10 m to 10 km long indicates that basic slip processes on the faults are scale invariant, and may be a cause for the inferred constant b-value for small earthquakes. Analysis of map-scale fault linkages and terminations indicate that linkage zones are up to 400 m wide and 1 km long, and consist of altered and fractured rocks with numerous through-going slip surfaces. Terminations are regions of numerous splay faults that have cumulative offsets approaching those of the main faults. The slip distribution and structure of the terminations and linkage zones suggest that seismic slip may propagate into these zones of enhanced toughness, and that through-going slip can occur when a sufficient linkage of faults in the zone allow slip to be transmitted

Effective crustal permeability controls fault evolution: An integrated structural, mineralogical and isotopic study in granitic gneiss, Monte Rosa, Northern Italy

Two dextral faults within granitic gneiss in the Monte Rosa nappe, northern Italy reveal key differences in their evolution controlled by evolving permeability and water/rock reactions. The comparison reveals that identical host rock lithologies develop radically different mineralogies within the fault zones, resulting in fundamentally different deformation histories. Oxygen and hydrogen isotope analyses coupled to microstructural characterisation show that infiltration of meteoric water occurred into both fault zones. The smaller Virgin Fault shows evidence of periodic closed system behaviour, which promoted the growth of hydrothermal K-feldspar, whilst the more open system behaviour of the adjacent Ciao Ciao Fault generated a weaker muscovite-rich fault core, which promoted a step change in fault evolution. Effective crustal permeability is a vital control on fault evolution and, coupled to the temperature (i.e. depth) at which key mineral transformations occur, is probably a more significant factor than host rock strength in controlling fault development. The study suggests that whether a fault in granitic basement grows into a large structure may be largely controlled by the initial hydrological properties of the host rocks. Small faults exposed at the surface may therefore be evolutionary “dead-ends” that typically do not represent the early stages in the development of larger faults

Increasing the quality of seismic interpretation

Acknowledgments E. Macrae was funded by an NERC Open CASE Ph.D. award (NE/F013728/1) with Midland Valley Exploration Ltd. as the industry partner. We thank 763 geoscientists for their participation, and in particular, the REs who gave their time freely to the project. M. Scott (University of Glasgow, UK) is thanked for assisting with the statistical analysis. Four reviewers are thanked for their constructive comments that improved the manuscript.Peer reviewedPublisher PD

Seismic slip on the west flank of the Upper Rhine Graben (France-Germany) : evidence from tectonic morphology and cataclastic deformation bands

Intraplate large and moderate earthquakes have occurred along the Upper Rhine Graben (URG) in the past but no coseismic surface faulting has been reported so far. We investigate the 25-km-long linear Riedseltz-Landau normal fault scarp affecting late Pleistocene and Holocene deposits of the western edge of the northern URG. The fault zone with cataclastic deformation textures is exposed in the Riedseltz quarry where it affects Pliocene and late Pleistocene (Wurm) units. Cataclasis is demonstrated by spalling and transgranular fractures in quartz grains concentrated in deformation bands with reduced grain size. The observed microstructures suggest multiple phases of deformation with cataclasis followed by emplacement of Fe-oxide matrix into deformation bands, and later emplacement of a clay-rick matrix into fractures. Previous studies along the fault show late Pleistocene (Wurm) loess deposits and early Holocene sand-silty deposits with 1.5 m and 0.7 m surface slip, respectively. New and previous results provide a minimum 0.15 mm/yr slip rate. A dislocation model suggests a minimum Mw 6.6 earthquake as a plausible scenario in the western edge of northern URG. Surface faulting in young sediments associated with cataclasis provides new evidence for assessing the occurrence of large earthquakes and seismic hazard assessment in the northern URG

Independent Expert Scientific Panel – Report on Unconventional Oil and Gas

No abstract available

Fracking bad language – hydraulic fracturing and earthquake risks

We thank all conference and event organis- ers for supporting our work, as well as survey participants. We also thank Stella Pytharouli, James Verdon, and Stephen Hicks, for their insights into earthquake magnitudes and seismological terminology, and Juan Alcalde for comments about language nuance and trans- lation. We would also like to thank Brigitte Nerlich for the early discussion about the relevance of this work.Peer reviewedPublisher PD

Wheat diseases in Western Australia

DISEASES caused by pathogenic organisms can seriously affect the yield of wheat. Some diseases are comparatively rare whereas others occur over a large area of the wheatbelt year after year