From University of Cambridge (UK) : “Rock crystals from the deep give microscopic clues to earthquake ground movements”

U Cambridge bloc

From University of Cambridge (UK)

24 Jun 2021
Erin Martin-Jones
cmm201@cam.ac.uk

1
Chunks of exotic green rocks from the mantle erupted from the San Carlos Volcanic Field, Arizona.
Credit: James St John.

Microscopic imperfections in rock crystals deep beneath Earth’s surface play a deciding factor in how the ground slowly moves and resets in the aftermath of major earthquakes, says new research involving the University of Cambridge.

The stresses resulting from these defects – which are small enough to disrupt the atomic building blocks of a crystal – can transform how hot rocks beneath Earth’s crust move and in turn transfer stress back to Earth’s surface, starting the countdown to the next earthquake.

The new study, published in Nature Communications, is the first to map out the crystal defects and surrounding force fields in detail. “They’re so tiny that we’ve only been able to observe them with the latest microscopy techniques,” said lead author Dr David Wallis from Cambridge’s Department of Earth Sciences, “But it’s clear that they can significantly influence how deep rocks move, and even govern when and where the next earthquake will happen.”

By understanding how these crystal defects influence rocks in the Earth’s upper mantle scientists can better interpret measurements of ground motions following earthquakes, which give vital information on where stress is building up – and in turn where future earthquakes may occur.

Earthquakes happen when pieces of Earth’s crust suddenly slip past each other along fault lines releasing stored-up energy which propagates through the Earth and causes it to shake. This movement is generally a response to the build-up of tectonic forces in the Earth’s crust, causing the surface to buckle and eventually rupture in the form of an earthquake.

Their work reveals that the way Earth’s surface settles after an earthquake, and stores stress prior to a repeat event, can ultimately be traced to tiny defects in rock crystals from the deep.

“If you can understand how fast these deep rocks can flow, and how long it will take to transfer stress between different areas across a fault zone, then we might be able to get better predictions of when and where the next earthquake will strike,” said Wallis.

The team subjected olivine crystals – the most common component of the upper mantle — to a range of pressures and temperatures in order to replicate conditions of up to 100 km beneath Earth’s surface, where the rocks are so hot (roughly 1250 deg C) they move like syrup.

Wallis likens their experiments to a blacksmith working with hot metal – at the highest temperatures, their samples were glowing white-hot and pliable.

They observed the distorted crystal structures using a high-resolution form of electron microscopy called electron backscatter diffraction, which Wallis has pioneered on geological materials.

Their results shed light on how hot rocks in the upper mantle can mysteriously morph from flowing almost like syrup immediately after an earthquake to becoming thick and sluggish as time passes.

This change in thickness — or viscosity – transfers stress back to the cold and brittle rocks in the crust above, where it builds up – until the next earthquake strikes.

The reason for this switch in behaviour has remained an open question, “We’ve known that microscale processes are a key factor controlling earthquakes for a while, but it’s been difficult to observe these tiny features in enough detail,” said Wallis. “Thanks to a state-of-the-art microscopy technique, we’ve been able to look into the crystal framework of hot, deep rocks and track down how important these miniscule defects really are”.

Wallis and co-authors show that irregularities in the crystals become increasingly tangled over time; jostling for space due to their competing force fields – and it’s this process that causes the rocks to become more viscous.

Until now it had been thought that this increase in viscosity was because of the competing push and pull of crystals against each other, rather than being caused by microscopic defects and their stress fields inside the crystals themselves.

The team hope to apply their work to improving seismic hazard maps, which are often used in tectonically active areas like southern California to estimate where the next earthquake will occur. Current models, which are usually based on where earthquakes have struck in the past, and where stress must therefore be building up, only take into account the more immediate changes across a fault zone and do not consider gradual stress changes in rocks flowing deep within the Earth.

Working with colleagues at Utrecht University [Universiteit Utrecht] (NL), Wallis also plans to apply their new lab constraints to models of ground movements following the hazardous 2004 earthquake which struck Indonesia, and the 2011 Japan quake – both of which triggered tsunamis and lead to the loss of tens of thousands of lives.

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

U Cambridge Campus

The University of Cambridge (UK) [legally The Chancellor, Masters, and Scholars of the University of Cambridge] is a collegiate public research university in Cambridge, England. Founded in 1209 Cambridge is the second-oldest university in the English-speaking world and the world’s fourth-oldest surviving university. It grew out of an association of scholars who left the University of Oxford(UK) after a dispute with townsfolk. The two ancient universities share many common features and are often jointly referred to as “Oxbridge”.

Cambridge is formed from a variety of institutions which include 31 semi-autonomous constituent colleges and over 150 academic departments, faculties and other institutions organised into six schools. All the colleges are self-governing institutions within the university, each controlling its own membership and with its own internal structure and activities. All students are members of a college. Cambridge does not have a main campus and its colleges and central facilities are scattered throughout the city. Undergraduate teaching at Cambridge is organised around weekly small-group supervisions in the colleges – a feature unique to the Oxbridge system. These are complemented by classes, lectures, seminars, laboratory work and occasionally further supervisions provided by the central university faculties and departments. Postgraduate teaching is provided predominantly centrally.

Cambridge University Press a department of the university is the oldest university press in the world and currently the second largest university press in the world. Cambridge Assessment also a department of the university is one of the world’s leading examining bodies and provides assessment to over eight million learners globally every year. The university also operates eight cultural and scientific museums, including the Fitzwilliam Museum, as well as a botanic garden. Cambridge’s libraries – of which there are 116 – hold a total of around 16 million books, around nine million of which are in Cambridge University Library, a legal deposit library. The university is home to – but independent of – the Cambridge Union – the world’s oldest debating society. The university is closely linked to the development of the high-tech business cluster known as “Silicon Fe”. It is the central member of Cambridge University Health Partners, an academic health science centre based around the Cambridge Biomedical Campus.

By both endowment size and consolidated assets Cambridge is the wealthiest university in the United Kingdom. In the fiscal year ending 31 July 2019, the central university – excluding colleges – had a total income of £2.192 billion of which £592.4 million was from research grants and contracts. At the end of the same financial year the central university and colleges together possessed a combined endowment of over £7.1 billion and overall consolidated net assets (excluding “immaterial” historical assets) of over £12.5 billion. It is a member of numerous associations and forms part of the ‘golden triangle’ of English universities.

Cambridge has educated many notable alumni including eminent mathematicians; scientists; politicians; lawyers; philosophers; writers; actors; monarchs and other heads of state. As of October 2020 121 Nobel laureates; 11 Fields Medalists; 7 Turing Award winners; and 14 British prime ministers have been affiliated with Cambridge as students; alumni; faculty or research staff. University alumni have won 194 Olympic medals.

History

By the late 12th century the Cambridge area already had a scholarly and ecclesiastical reputation due to monks from the nearby bishopric church of Ely. However it was an incident at Oxford which is most likely to have led to the establishment of the university: three Oxford scholars were hanged by the town authorities for the death of a woman without consulting the ecclesiastical authorities who would normally take precedence (and pardon the scholars) in such a case; but were at that time in conflict with King John. Fearing more violence from the townsfolk scholars from the University of Oxford started to move away to cities such as Paris; Reading; and Cambridge. Subsequently enough scholars remained in Cambridge to form the nucleus of a new university when it had become safe enough for academia to resume at Oxford. In order to claim precedence it is common for Cambridge to trace its founding to the 1231 charter from Henry III granting it the right to discipline its own members (ius non-trahi extra) and an exemption from some taxes; Oxford was not granted similar rights until 1248.

A bull in 1233 from Pope Gregory IX gave graduates from Cambridge the right to teach “everywhere in Christendom”. After Cambridge was described as a studium generale in a letter from Pope Nicholas IV in 1290 and confirmed as such in a bull by Pope John XXII in 1318 it became common for researchers from other European medieval universities to visit Cambridge to study or to give lecture courses.

Foundation of the colleges

The colleges at the University of Cambridge were originally an incidental feature of the system. No college is as old as the university itself. The colleges were endowed fellowships of scholars. There were also institutions without endowments called hostels. The hostels were gradually absorbed by the colleges over the centuries; but they have left some traces, such as the name of Garret Hostel Lane.

Hugh Balsham, Bishop of Ely, founded Peterhouse – Cambridge’s first college in 1284. Many colleges were founded during the 14th and 15th centuries but colleges continued to be established until modern times. There was a gap of 204 years between the founding of Sidney Sussex in 1596 and that of Downing in 1800. The most recently established college is Robinson built in the late 1970s. However Homerton College only achieved full university college status in March 2010 making it the newest full college (it was previously an “Approved Society” affiliated with the university).

In medieval times many colleges were founded so that their members would pray for the souls of the founders and were often associated with chapels or abbeys. The colleges’ focus changed in 1536 with the Dissolution of the Monasteries. Henry VIII ordered the university to disband its Faculty of Canon Law and to stop teaching “scholastic philosophy”. In response, colleges changed their curricula away from canon law and towards the classics; the Bible; and mathematics.

Nearly a century later the university was at the centre of a Protestant schism. Many nobles, intellectuals and even commoners saw the ways of the Church of England as too similar to the Catholic Church and felt that it was used by the Crown to usurp the rightful powers of the counties. East Anglia was the centre of what became the Puritan movement. In Cambridge the movement was particularly strong at Emmanuel; St Catharine’s Hall; Sidney Sussex; and Christ’s College. They produced many “non-conformist” graduates who, greatly influenced by social position or preaching left for New England and especially the Massachusetts Bay Colony during the Great Migration decade of the 1630s. Oliver Cromwell, Parliamentary commander during the English Civil War and head of the English Commonwealth (1649–1660), attended Sidney Sussex.

Modern period

After the Cambridge University Act formalised the organisational structure of the university the study of many new subjects was introduced e.g. theology, history and modern languages. Resources necessary for new courses in the arts architecture and archaeology were donated by Viscount Fitzwilliam of Trinity College who also founded the Fitzwilliam Museum. In 1847 Prince Albert was elected Chancellor of the University of Cambridge after a close contest with the Earl of Powis. Albert used his position as Chancellor to campaign successfully for reformed and more modern university curricula, expanding the subjects taught beyond the traditional mathematics and classics to include modern history and the natural sciences. Between 1896 and 1902 Downing College sold part of its land to build the Downing Site with new scientific laboratories for anatomy, genetics, and Earth sciences. During the same period the New Museums Site was erected including the Cavendish Laboratory which has since moved to the West Cambridge Site and other departments for chemistry and medicine.

The University of Cambridge began to award PhD degrees in the first third of the 20th century. The first Cambridge PhD in mathematics was awarded in 1924.

In the First World War 13,878 members of the university served and 2,470 were killed. Teaching and the fees it earned came almost to a stop and severe financial difficulties followed. As a consequence the university first received systematic state support in 1919 and a Royal Commission appointed in 1920 recommended that the university (but not the colleges) should receive an annual grant. Following the Second World War the university saw a rapid expansion of student numbers and available places; this was partly due to the success and popularity gained by many Cambridge scientists.