On 16 November next month, RSES will be celebrating a significant milestone – the 50th Birthday of our first high temperature high pressure rock deformation apparatus, developed and built in-house by Professor Mervyn Paterson. These apparatus marked a major global advance in the ability to measure and understand the strength, rheology and behaviour of earth materials at pressures and temperatures equivalent to depths of 20km in the crust. Even today, 50 years on, these gas medium apparatus remain relevant, achieving unsurpassed mechanical accuracy at high pressure-temperature conditions.
Many of us have seen Professor Mervyn Paterson, now aged 92, at tea and around the School – but who was he and what did he do that was so significant? Mervyn spent his career working as geophysicist and instrument developer, specializing in rock deformation. He was born into a farming family in South Australia in 1925 and attended the Adelaide Technical High School. In 1943 he completed his undergraduate studies in metallurgy at the University of Adelaide. Mervyn began his career at the CSIR Division of Aeronautics working on the physics of metal fatigue in a position that would now be called a ‘materials scientist’. He received a PhD from the University of Cambridge in the UK on x-ray diffraction effects of deformation in metals, and pursued postdoctoral studies in Chicago in the USA.
In 1951 Mervyn returned to Australia to work at the newly-named CSIRO, but was soon approached by Professor John Jaeger and appointed to pursue research in the field of experimental rock deformation within the Department of Geophysics at the Australian National University. Commencing in 1953, Mervyn remained as a researcher at the subsequently formed Research School of Earth Sciences until his retirement in 1990. During this time he developed the instruments that we have today in the High Pressure Rock Physics Lab and undertook seminal research into the strength and behavior of many crustal materials including work on quartz, calcite and olivine. Following ‘retirement’ Mervyn proceeded to have a second career as the chairman of Paterson Instruments Pty Ltd, a company which oversaw the development of all the ‘commercial’ Paterson apparatus that are the pride of many rock deformation labs around the world. Not one to take retirement too easily, Mervyn published his last book at the age of 88, titled ‘Materials Science for Structural Geology’.
The Rock Physics lab at RSES is in the fortunate position of being the envy of many experimental rock physicists, with an unprecedented three (3) high temperature, high pressure gas apparatus. These include two deformation apparatus and the attenuation apparatus, which is used to measure seismic properties of rocks at crustal to mantle conditions. When thinking about national infrastructure and capacity, it is worth highlighting that we are the only rock physics lab with ability to explore high pressure, high temperature, fluid saturated conditions in the Southern Hemisphere.
But what makes these machines so special? Central to the operation of these machines is the pressure vessel – a big cylinder of steel that can be pressurized. We use argon gas as the medium that we pressurize to between 3000 to 5000 atmospheres (300-500 MPa or, for our petrologist friends, 3-5 kbar). Inside the pressure vessel we have a furnace that raises the temperature as high as 1300 °C. A load or force is applied to the sample, making it deform either plastically or by brittle failure, forming miniature ‘labquakes’. During deformation, the applied forces are measured inside the pressure vessel, giving unrivaled accuracy of the mechanical data. In particular, internal measurement removes effects such as the frictional contribution of the high pressure seals. Although the design is seemingly quite simple, Mervyn’s machines remain the only gas-medium apparatus that can operate in the given P-T space. As a number of other researchers have discovered to their dismay when trying to build an equivalent, the devil is in the detail!
Rig 1 is technically not the first pressure vessel of its kind at ANU, but rather it is the oldest surviving one. In the early days of rock deformation, people did not fully understand the effects of corrosion, hydrogen embrittlement and pressure cycling on strength of the apparatus. It was also during the heady days of pumping gas to 1 GPa (10 kbar) and on one fine morning in 1964 the first pressure vessel on Rig 1 exploded…
Thankfully Mervyn had designed and built the lab planning for the worst. The machine was contained within a bunker with 30 cm thick concrete walls. No one was injured and there was surprisingly little damage (except to the pressure vessel). The shards of the vessel can still be found in the lab and serve as a reminder to all users of what can happen.
You might be thinking that after 50 years of service Rig 1 might be due for retirement. Nothing could be further from the truth and it remains as relevant today as when it was built. One of Rig 1’s main assets is versatility: over the past decades it has been a platform for numerous research ventures ranging from meticulously defining rheological properties of earth materials to my current research interests exploring the first stages of earthquake slip.
In 2015 an innovative partnership was established with physicists from the Department of Quantum Physics to build a unique measurement system to capture, for the first time, the mechanical behavior of tiny earthquakes produced in the lab. We combined Nobel Prize-winning technology used for the detection of gravity waves, with the unique pressure and temperature environment provided by Rig 1. With this capability we are now begining to unravel the secrets of earthquake initiation at realistic mid crustal-conditions – one of the great unresolved enigmas of geophysics. In 2016 this endeavor captured the attention of the Major Equipment Committee and the project was awarded a grant that has allowed continued development, and culminated in an instrument that is truly globally unique. The up-coming Birthday Party is an opportunity to celebrate not only the wonderful and rich history of this machine but also to showcase its exciting future.
Former lab users and guests will be coming from around the world to mark the occasion of the 50th anniversary of the first use Rig 1. On 16 November we will be having a series of seminars with talks given by our visitors and current lab users. The day will start with tours of the High Pressure Rock Physics Laboratory – so please join in and visit one of RSES’s hidden gems! Following the tours there will be a school morning tea. Details of the seminar program will be posted shortly and everyone is very welcome to attend.
References: Lambeck, K., Paterson, M. 2006 ‘Professor Mervyn Paterson, geophysicist’ Interviews with Australian Scientists, Australian Academy of Science.