Chairs
Dr Alex Copley, University of Cambridge, UK
Professor Lucy Flesch, Purdue University, USA
Dr Alex Copley, University of Cambridge, UK
Dr Copley is an Earth Scientist working in the University of Cambridge, studying tectonics from the scale of individual fault systems to large mountain ranges. His work spans observations of deformation (using seismology, InSAR, field and remote sensing observations of geology and geomorphology), and numerical modelling to understand the underlying forces at work. Areas of particular interest include continental deformation and the rheology of the lithosphere.
Professor Lucy Flesch, Purdue University, USA
Lucy Flesch is a Professor in the Department of Earth, Atmospheric and Planetary Sciences at Purdue University. Her research integrates geodetic, seismic, and geologic observations into geodynamic models to address questions relating to how strain is accommodated across large zones of continental deformation, rheology of the lithosphere, lithospheric coupling, role of gravitational potential energy and the balance of forces responsible for generating observed deformation. Professor Flesch has written papers addressing these questions for the India-Eurasia collision zone, Western United States, Alaska, Africa and South America. Professor Flesch received her PhD in 2002 from Stony Brook University working with Bill Holt.
09:00-09:05
Welcome by the Royal Society and organisers
09:05-09:30
Geophysical imaging of fault-zone rheology
Professor Roland Bürgmann, University of Berkeley, USA
Abstract
Fault-zone rheology governs the mechanics of faults and the earthquake cycle and determines the hazards arising from fault slip in the Earth’s crust. Our knowledge of the frictional and bulk rheology of crustal fault zones has traditionally been based on laboratory rock mechanics experiments. However, such experiments have to be carried out at spatial and temporal scales that are very far from those found in nature. It is also possible to probe the mechanical properties of fault zones using geodetic and seismological observations of fault zones during transient periods of postseismic afterslip, fault slip and microseismicity modulated by tides and seasonal loads, and spontaneous slow slip events. These deformation episodes can thus serve as natural laboratory experiments that improve understanding of the mechanics of fault slip. Recent advances in space geodetic observations and seismological techniques have helped better illuminate fault-zone properties. As the data improve, increasingly physical models should be developed to determine fault zone properties. To better understand fault-zone structure and properties, it is also important to consider geological field observations of fault zones exhumed from varying tectonic settings and depths. Thus, to further this type of research it is essential to optimize and integrate a wide variety of observations. A number of recent examples are used to illustrate the promises and challenges of geophysical probing of fault-zone behaviour and rheology.
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Professor Roland Bürgmann, University of Berkeley, USA
Professor Roland Bürgmann, University of Berkeley, USA
Roland Bürgmann received his Vordiplom in Geology at the Universität Tübingen, Germany, in 1987, his MS at the University of Colorado, Boulder, in 1989, and his PhD at Stanford University, in 1993. He is currently Professor at the Department of Earth and Planetary Science at UC Berkeley. His research interests are in active tectonics, crustal deformation and lithosphere rheology. Bürgmann’s research group uses space-geodetic measurements, seismic data, and field observations to constrain crustal deformation associated with active faults, volcanoes, fluid reservoirs, and landslides. He is a Fellow and 2013 Birch lecturer of the American Geophysical Union (AGU). He is currently chairing the National Earthquake Prediction Evaluation Council (NEPEC) and is a member of NASA’s Earth Science Advisory Committee (ESAC). See http://seismo.berkeley.edu/~burgmann/ for more information about Bürgmann’s research and publications.
09:45-10:15
Relations between earthquake distributions, geological history, tectonics and rheology
Professor James Jackson CBE FRS, University of Cambridge, UK
Abstract
A first-order feature of the geological history of continents is the contrast between the long-lived stability of the ancient continental interiors and the widespread deformation in Phanerozoic orogenic belts; displayed most obviously in the asymmetry of the India-Asia collision. Through advances in seismic tomography, we can now make increasingly detailed maps of the variations in lithosphere (plate) thickness on the continents. The variations are dramatic, with some places up to 300 km thick, and clearly relate to the geological history of the continents as well as their present-day deformation. Where the lithosphere thickness is about 120 km or less continental earthquakes are generally confined to upper crustal material that is colder than about 350oC. On the edge of thick lithosphere, the entire crust may be seismogenic, with earthquakes sometimes extending into the uppermost mantle if the Moho is colder than 600oC; but the continental mantle is generally aseismic. In such regions, earthquakes in the continental lower crust at 400-600oC require the crust to be anhydrous (granulite facies) and are a useful guide or proxy to both composition and strength. These correlations have important implications for the geological evolution of the continents. They can be seen to have influenced features as diverse as: the location of post-collisional rifting; intracratonic basin formation; the location, origin and timing of granulite metamorphism; and the formation, longevity and strength of cratons. In addition, they have important consequences for earthquake hazard assessment on the slowly deforming edges of continental shields or platforms, where the large seismogenic thickness can host very large earthquakes.
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Professor James Jackson CBE FRS, University of Cambridge, UK
Professor James Jackson CBE FRS, University of Cambridge, UK
James Jackson is a Professor in the Department of Earth Sciences in the University of Cambridge. He was born and raised in India, which established his interest in all aspects of Asia, where much of his research has been concentrated. He uses seismology, geodesy, and Quaternary geology, combined with observations of the landscape in the field, to study how the continents develop and deform on all scales, from the movement that occurs in individual earthquakes to the evolution of mountain belts. His field work has taken him to many parts of Asia, the Mediterranean, Africa, New Zealand and North America. He is increasingly involved in how to use earthquake science to reduce the appalling risk from earthquakes to populations in developing countries, and co-led the project ‘Earthquakes Without Frontiers’ (www.ewf.nerc.ac.uk).
11:00-11:30
Earthquakes and mountain building in the Himalaya
Professor Jean-Philippe Avouac, California Institute of Technology, USA
Abstract
Earthquakes are deformation increments that must contribute to build geological structures and topography in the long run. The Himalaya is one place where this process can be observed at play. Crustal shortening is active and has produced a well-expressed thrust system and the highest topography on Earth today. It might have come as a surprise that, a result of both coseismic subsidence and intense mass wasting by landslides, the high Himalaya went down during the 2015, Mw7.8 Gorkha earthquake. Modelling shows that, in the Himalayan context, the topography actually builds up in the time period between large earthquakes due to thermally enhanced aseismic deformation. This kinematics results from the ramp-and-flat geometry and thermal structure of the thrust system, which in turn are the result of coupling between crustal deformation and erosion over the long-term. This framework reconciles the geological and topographic expression of the Himalaya with its current activity. Within this framework, various types of observations can be used to inform rheological properties. A low effective friction is necessary to allow slip with little heat production on the sub-horizontal décollement beneath the lesser Himalaya. Given that the décollement was locked before the Gorkha earthquake and didn’t produce any significant afterslip, the low friction is likely due to dynamic weakening during seismic sliding. Observations of post-seismic relaxation, crustal rebound following lake regression in south Tibet, and gravity can be used to constrain further the rheology of the crust and mantle lithosphere across the Himalaya and southern Tibet.
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Professor Jean-Philippe Avouac, California Institute of Technology, USA
Professor Jean-Philippe Avouac, California Institute of Technology, USA
Jean-Philippe Avouac is the Earle C. Anthony Professor of Geology and of Mechanical and Civil Engineering at the California Institute of Technology, and director of the NSF center for Geomechanics and the Mitigation of Geohazards. He received his PhD in from the Institut de Physique du Globe de Paris, France, in 1991. He worked at the Commissariat à l’Energie Atomique, France, from 1991 to 2001. He was the director of the Tectonics Observatory at the California Institute of Technology from 2004 to 2014. He worked as the BP-McKenzie Professor of Earth Sciences at the University of Cambridge from 2014 to 2015.
Jean-Philippe Avouac studies crustal deformation, earthquakes in particular, and geomorphic processes. He has contributed to method developments in remote sensing, geodesy, geomorphology and seismology. Jean-Philippe Avouac has published over 190 articles in international peer-reviewed journals (Google scholar profile) and holds patents in remote sensing.
11:45-12:15
The relation between long and short term deformation in actively deforming plate boundary zones
Dr Simon Lamb, Victoria University of Wellington, New Zealand
Abstract
It is now possible with satellite-based systems to monitor deformation of the Earth’s surface at high spatial resolution over periods of several decades and a significant fraction of the seismic cycle. The relation between deformation at this short timescale and long-term geological faulting, over 10s to 100s kyrs, is examined for subduction, continental shortening and rift settings, using examples from the active New Zealand and Central Andean plate boundary zone. Simple models of locking on a deep-seated megathrust or decollement, or mantle flow, provide excellent fits to the short-term observations without requiring any information about the geometry and rate of surface faulting. The short-term deformation in these examples cannot be used to determine the long term behaviour of individual faults, but instead places constraints on the forces that drive deformation. Thus, there is a fundamental difference between the stress loading and stress relief parts of the earthquake cycle, with failure determined by dynamical rather than kinematic constraints; the same stress loading can give rise to widely different modes of long-term deformation, depending on the strength and rheology of the deforming zone, and the role of gravitational stresses. The process of slip on active faults may have an intermediate timescale of kyrs to 10s kyrs, where faults fail piecemeal without any characteristic behaviour. Physics-based dynamical models of short-term deformation may be the best way to make full use of the increasing quality of this type of data in the future.
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Dr Simon Lamb, Victoria University of Wellington, New Zealand
Dr Simon Lamb, Victoria University of Wellington, New Zealand
Simon Lamb completed his undergraduate and postgraduate degrees at Cambridge University. His doctoral thesis, supervised by Dr Alan Smith, was on the geological evolution of some of the oldest known supracrustal rocks in the Barberton Mountain Land of Swaziland. He switched to the other end of the geological timescale for his postdoctoral research, studying the mechanisms of tectonic rotations about a vertical axis in New Zealand, working with Professor Dick Walcott. Subsequently he was in the Department of Earth Sciences at Oxford University for over 20 years, first as a Royal Society University Research Fellow, then University Lecturer, leading a multidisciplinary project studying the tectonics of the Central Andes. Since 2010, he has been Associate Professor in Geophysics at Victoria University of Wellington, New Zealand, focusing on the tectonics of the New Zealand plate-boundary zone and integrating short term GPS observations with the longer term geological evolution.