In Adolescence, Owen Cooper captured the attention of audiences as an adolescent killer, whose character goes through a brilliant emotional arc. At just 15 years old, the child actor won best supporting actor in a limited/anthology series or TV movie for his work in the limited series. Previously, Scott Jacoby held the record, after winning the Primetime Emmy in 1973 at 16 years old, for his role in That Certain Summer.
The series took home Emmys for Stephen Graham in Lead Actor and Writing (alongside Jack Thorne), Owen Cooper for Supporting Actor, Erin Doherty for Supporting Actress, and Philip Barantini for Directing. It also secured wins in the overall Directing and Writing categories.
Elsie Booth hailed the atmosphere at the Brentwood Centre on Monday
Snooker fans have travelled from far and wide to watch the game’s finest players compete in the English Open.
The tournament heated up on Monday as seeded players joined the fight for its £100,000 jackpot.
World champion Zhao Xintong and title holder Neil Robertson are among the big names battling it out at the Brentwood Centre until Sunday.
But what do the people visiting Essex for the competition think of the venue?
James Patient/BBC
Xianghao Xiao was excited to meet three-time UK champion Ding Junhui
University student Xianghao Xiao was delighted to meet his fellow Chinese compatriot and three-time UK champion Ding Junhui.
“It’s fantastic for me,” said the 24-year-old, who grabbed a selfie with Junhui. “He’s very famous in China.
“Today is the first time I’ve seen him in person, so it’s very exciting.”
James Patient/BBC
Kumar Kuppusamy said being in Brentwood was a “nice experience”
It was also the first match Kumar Kuppusamy, 26, had watched in the UK.
He said: “It was a nice experience for me.”
World number 33 Matthew Selt, from Chelmsford, progressed into the next round after winning his first tie on Monday.
Also among the victors was Barry Hawkins, who saw off Louis Heathcote.
Chris Lamb, 65, travelled from south London to watch Hawkins, who he sponsored as a relative unknown.
“It’s a good venue to watch snooker,” he said of the Brentwood Centre.
Tom Williams/BBC
The tournament started on Thursday, but seeded players entered the fray on Monday
It was Elsie Booth’s first time in Essex, travelling east from Bristol to watch the action.
“I heard Brentwood was a nice place,” the 24-year-old said. “So it’s a nice occasion to come down for and it’s a good atmosphere.”
Among those making the noise was Neil Mortimer, 31, who bagged himself a front-row ticket and also managed to meet Junhui.
“His mentality on and off the table is so relaxing and peaceful,” said the east Londoner.
“It was really great to ask him a few questions and he was so welcoming to us.”
James Patient/BBC
Faisal Labban also got to meet Ding Junhui
His friend from the US, Faisal Labban, added: “To be able to see Ding in person, meet with him, take a picture and watch him get a century – it’s pretty cool.”
It was a much shorter journey for Basildon boy Stuart Bingham, who came down ahead of his opener on Tuesday.
The 2018 champion said it took him 27 minutes to get to Brentwood.
“It’s nice to commute back home, see the kids, see the dog and have a normal life,” he added.
Social media companies will be required to take “reasonable steps”, such as deactivating underage accounts, to comply with Australia’s under-16 social media ban, but they won’t be compelled to verify the age of all users.
Communications Minister Anika Wells and eSafety Commissioner Julie Inman Grant on Tuesday unveiled guidance for platforms to comply with the social media age restrictions that are set to come into effect on 10 December.
Under the guidelines, they must take certain “reasonable steps” through a “multilayered waterfall approach” to prevent children under 16 from holding accounts on their services.
Failure to do so could attract fines of up to $49.5 million.
Minister for Communications Anika Wells said platforms have the information they need to comply with the new laws. Source: AAP / Mick Tsikas
“This industry guidance makes clear our strong expectations that social media platforms step up to the plate to implement the minimum age in a way that is effective, private, and fair on Australian users,” Wells said.
“The government has done the work to ensure that platforms have the information they need to comply with the new laws — and it’s now on them to take the necessary steps.”
What steps are expected from platforms?
The guidance sets out examples of “reasonable steps” companies must take to comply with the age restrictions.
These include detecting and deactivating existing underage accounts and preventing circumvention by users who have had their accounts deactivated or removed.
Platforms should take what Inman Grant called a “multilayered waterfall approach” to age assurance to minimise “friction” with users and provide “accessible review mechanisms” for those who believe they’ve been wrongly flagged.
“Our principles-based guidance recognises that there is no one-size-fits-all solution for industry, given the diversity of platforms and technology and to help technology companies meet their obligations in a way that is effective, privacy-preserving and fair,” Inman Grant said.
Under the new guidance, platforms will not be required to use specific technologies, including those tested in the recent age assurance trial.
A report released by the government earlier this month argued age assurance technology can be implemented “efficiently and effectively” but noted these methods have a margin of error.
Inman Grant said most age-restricted social media platforms have already developed their own tools around age assurance, while the trial offers some additional options.
The guidelines also forbid relying solely on user age declarations and mandate that platforms continuously monitor and improve systems over time.
Unexpected guideline inclusions
Social media platforms will not be required to verify the age of all users, with blanket age verification considered “unreasonable”.
Platforms cannot compel users to provide government ID as the sole method to prove their age online, and must always offer reasonable alternatives.
They are also not expected to keep personal information from individual age checks, with record-taking to focus on systems and processes.
The guidance was developed by eSafety in consultation with industry and community stakeholders and informed by “broad” evidence including the age assurance trial, the government said.
When will the ban come into effect?
The law will come into effect from 10 December this year.
Inman Grant said companies should first focus on deactivating or removing accounts of under-16s, and making user reporting available.
“We also recognise that preventing future under-16s from joining platforms will take longer and be more complex,” she said.
Wells said social media companies will have had 12 months’ notice to comply with Australian law, “as we expect any company who conducts their business on these shores to do”.
When it comes to enforcement, Inman Grant said authorities would first engage informally with platforms to raise any concerns.
“There are, of course, certain companies that aren’t willing to engage, or will be likely to move to judicial review or a lawsuit. We need to be prepared for that as well,” she said.
“But in most cases, these companies want to operate in Australia and they respect Australian law.”
eSafety Commissioner Julie Inman Grant said the guidance encourages platforms to work collaboratively with eSafety to ensure compliance. Source: AAP / Mick Tsikas
Which platforms are included?
The government has previously said that age-restricted social media platforms will include Facebook, Instagram, Snapchat, TikTok, X and YouTube, among other platforms.
When the legislation was passed by parliament last November, YouTube was one of a handful of platforms listed as exempt because they were “out of scope” of the policy.
However, Inman Grant later wrote to Wells, making a formal recommendation that YouTube be included among the banned platforms.
Online gaming, messaging apps, health and education services won’t be included.
A ‘monumental event’ for children
Inman Grant acknowledged the upcoming ban will be a “monumental event” for a lot of children.
“A lot of children welcome this, as certainly parents do. But we know this will be difficult for kids,” she said.
However, she said companies around the world are moving towards age assurance technology, including online gaming site Roblox and dating app Tinder.
“All of this is creating an ecosystem that suggests this is the way the world is going.”
Colibactin, a mutagen produced by bacteria, is a likely contributor to the increasing incidence of early-onset colorectal cancer, according to the results of a genetic analysis of cancers from patients in intermediate- and high-incidence countries around the world.
The study “provides the strongest evidence to date that colibactin … causes specific DNA mutations that can initiate colorectal cancer,” according to senior author Ludmil Alexandrov, PhD, a professor in the Departments of Cellular and Molecular Medicine and Bioengineering at the University of California, San Diego. The investigators “identified a clear mutational signature linked to colibactin and showed that it is present in a substantial proportion of CRC tumors, particularly early-onset cases.”
Characterization of the drivers of early-onset CRC is a gap in the current literature, according to Samir Gupta, MD, a professor in the Division of Gastroenterology and the co-lead of the Cancer Control Program at UC San Diego Moores Cancer Center. He noted that “there has been a dramatic relative increase in incidence of young-onset CRC, with each generation born since 1960 experiencing higher risk for early-onset CRC than the prior. Further, it looks now that increased risk is being carried forward to middle age.” Dr. Gupta cited changes in obesity, alcohol exposure and diet as potential contributing factors, but said “environmental exposures have been largely unexplored.”
Study Details
Dr. Alexandrov and his co-investigators performed whole-genome sequencing on CRC samples from adults with no prior treatment for CRC from 11 countries in Asia, Europe, North America and South America (Nature 2025;643[8070]: 230-240).
Among 981 cases of CRC, 45.7% occurred in women and 132 were early-onset cancer. Cancers were evenly distributed across the proximal colon (320 cases), distal colon (333 cases) and rectum (326 cases), with two cases in unspecified sites. The early-onset cases were more common in the distal colon and rectum relative to the proximal colon.
After sequencing, the cancers were divided into microsatellite stability (MSS) and microsatellite instability samples, which were DNA mismatch repair-proficient and -deficient, respectively. The investigators focused their main analyses on the MSS samples (81.8%, 802 total, 97 early-onset cancer).
Among these MSS samples, single base substitutions (SBS) and small insertions and deletions (ID) were less common among early-onset cases than they were in cases in patients aged 50 years and older (SBS fold-change, 0.92; P=0.045; ID fold-change, 0.90; P=0.018), although the average SBS and ID mutation spectra of early- and late-onset cases were similar. There were no statistically significant differences in the burden of average mutational spectra of doublet base substitutions, copy number alterations or structural variants in early- and late-onset cases.
The mutational profiles of the cancers across the 11 countries were generally similar, but the investigators identified certain mutational signatures that were more prevalent in individual countries. They further explored how these different mutational signatures were related to age-standardized CRC incidence rates (ASR) to better understand of the implications of different mutational processes. Of note, colibactin-induced mutational signatures (SBS88 and ID18), among others, were associated with increased ASR overall as well as early-onset cancer.
Defined as the presence of either SBS88 or ID18, colibactin exposure was found in 21.1% of the 802 MSS samples. SBS88 and ID18 were, respectively, 2.5 (Q=0.006) and 4 (Q=3.7’10-7) times as common in early-onset cases than in cases diagnosed in patients 50 years of age and older. These colibactin-induced signatures became less common as age of diagnosis increased. The median age of diagnosis specifically in the distal colon and rectum was lower in the colibactin-exposed patients than in the unexposed group (distal: 57 vs. 66 years; Q=5.2’10-7; rectum: 63 vs. 66 years; Q=0.025).
The investigators also assessed the clonal structure of the samples to characterize mutations as early clonal, late clonal or subclonal during CRC development. The colibactin-induced signatures were found to be enriched in early rather than late clonal mutations, which the investigators noted was “consistent with the presence of these mutational signatures in normal colorectal epithelium.” This early clonal enrichment was found in both early- and late-onset cancer cases.
When assessing the contribution of SBS88 and ID18 to driver gene mutations, the investigators found that, among colibactin-exposed cases, 8.3% of all SBS and ID driver mutations and 15.5% of APC driver mutations could be accounted for by colibactin-induced mutations. The researchers found no difference between early- and late-onset cases.
Bacteria that carry the pks pathogenicity island produce colibactin. Thus, the investigators assessed whether patients with colibactin-induced mutations had pks+ bacteria. They found no association between the mutations and bacteria presence, which they said could be due to “imprinting of SBS88 and ID18 on the colorectal epithelium during an early period of life when pks+ bacteria were present, followed by the natural plasticity of the microbiome over subsequent decades, leading to the loss of pks+ bacteria.”
Key Takeaways
Dr. Alexandrov noted the importance of further research to better understand the role of colibactin exposure in CRC carcinogenesis, including characterizing “the timing, duration and frequency of exposure” to colibactin-producing bacteria and understanding how “the interplay between host genetics, immune response, microbiome composition and environmental factors” informs susceptibility to colibactin-induced mutations and carcinogenesis.
Dr. Gupta also stressed the importance of additional research to “explore what might be driving the increased exposure to colibactin-generating bacteria,” as well as “what may be driving some of the mutational patterns that were overrepresented in early-onset CRC, for which the upstream drivers remain completely unexplained.”
Dr. Alexandrov said his team’s work “suggests that bacterial exposures in the gut, particularly during childhood or early life, may play a previously underappreciated role in driving colorectal tumorigenesis.” These findings “highlight the potential for future” screenings and interventions, he added, including “stool-based screening tools that detect colibactin-induced DNA damage long before cancer develops” and “the possibility that modulating the microbiome in childhood—through antibiotics, probiotics or dietary interventions—might eventually reduce CRC risk in high-risk individuals.”
—Natasha Albaneze, MPH
Dr. Alexandrov reported financial relationships with Acurion and Inocras. He holds European Patent Application No. EP25305077.7, which focuses on using the colibactin mutational signature in stool samples for the detection of early-onset colorectal cancer. Dr. Gupta reported no relevant financial disclosures.
This article is from the September 2025 print issue.
CEOs call for a new era of pragmatic execution that embeds sustainability in strategy and culture (96%), but warn of capability gaps in technology and communications.
NEW YORK, Sept. 16, 2025 /PRNewswire/ — United Nations — CEOs shift from ambition to activation on sustainability, with nearly all (99%) stating their intent to maintain or expand their commitments, according to the 2025 edition of the CEO Study from the United Nations Global Compact and Accenture. Despite only a small percentage (fewer than 15%) feeling well prepared for major global challenges, including inflation, trade and climate change, a majority (88%) of CEOs say the business case for sustainability is stronger than it was five years ago.
Unlocking the Next Era of Sustainability Leadership
“Turning the Key: Unlocking the Next Era of Sustainability Leadership” comes at a critical time, as 2024 marks the first calendar year to exceed the Paris Agreement’s 1.5°C threshold. The report offers one of the most comprehensive longitudinal views of CEO sentiment on sustainability, published as the UN Global Compact celebrates its 25th anniversary.
Commenting on the study’s findings, Sanda Ojiambo, CEO and Executive Director of the UN Global Compact said: “CEOs are crystal clear: sustainability has moved from moral imperative to business fundamental. This study sets out a pragmatic playbook: work with regulators, meet fast-rising consumer expectations, invest in technology and skills, and communicate progress credibly. As the world breached the 1.5°C threshold and with a $4.3 trillion annual SDG financing gap leaving 3.4 billion people in countries spending more on interest than on health or education, the private sector must close the execution gap—embedding sustainability into strategy and culture, scaling innovation across value chains, and partnering to shape rules that reward long-term business value. Companies that act on these findings will build resilience, unlock growth, grow industries, stimulate economies and accelerate delivery of the Sustainable Development Goals.”
The 2025 CEO Study distills five “keys” to unlock momentum at scale: collaborate on regulation; harness consumer demand; expand access to technology; upskill for the future; and lead with credibility and purpose. CEOs are already preparing for a more regulated future—92% say strong global governance and unified policy are important or critical; 95% report regulatory compliance is a leading organizational priority; and 84% believe their companies are ready to meet upcoming sustainability regulations.
At the same time, consumer influence is gaining ground, alongside that of governments, employees and even investors. Ninety-eight per cent agree the private sector can drive progress through sustainable products and services, and 96% of CEOs advise their successors to embed sustainability in the company vision and culture. But gaps persist, particularly around digital tools to track and measure sustainability performance across value chains, which can limit how fully companies are able to respond to rising demand.
The report further finds that governance and technology-based skills for forward-looking risk capabilities are also lagging: only one in four (26%) CEOs report having dedicated scenario-planning teams and even less (fewer than 15%) feel well-prepared for major macroeconomic and sustainability challenges. And while 96% of CEOs say innovation and technology are essential to achieving global sustainability goals, 27% are considering leveraging digital tools for sustainability tracking and measurement.
“Business leaders know that technology, data and AI are critical to meeting their sustainability targets, yet gaps persist as they move from ambition to execution,” said Stephanie Jamison, Global Resources Industry Practice Chair and Global Sustainability Services Lead at Accenture. “Across industries and geographies, our clients are eager to move away from isolated projects toward adopting a multigenerational approach that compounds learnings, accelerates delivery and reduces cost. This can be a blueprint for growth that pairs sustainability commitments with bold, AI-driven reinvention that is built-in, not bolted on.”
Notes to Editors
About the CEO Study Program The CEO Study Program, developed by the UN Global Compact in collaboration with Accenture, is one of the largest global studies of CEO sentiment on sustainability. Through a quantitative assessment of nearly 2,000 CEOs and in-depth one-to-one interviews with CEOs, chairpersons and presidents of UN Global Compact member companies, this research coalesces perspectives to analyze key developments and emerging trends in sustainability. The CEO Study report is an extensive review of the advancing corporate sustainability movement aimed at accelerating progress for the UN Sustainable Development Goals.
About the UN Global Compact The ambition of the UN Global Compact is to accelerate and scale the global collective impact of business by upholding the Ten Principles and delivering the SDGs through accountable companies and ecosystems that enable change. With more than 20,000 participating companies, 5 Regional Hubs, 64 Country Networks covering 85 countries and 9 Country Managers establishing Networks in 16 other countries, the UN Global Compact is the world’s largest corporate sustainability initiative—one Global Compact uniting business for a better world. For more information, follow @globalcompact on social media and visit our website at unglobalcompact.org.
About Accenture Accenture is a leading global professional services company that helps the world’s leading businesses, governments and other organizations build their digital core, optimize their operations, accelerate revenue growth and enhance citizen services—creating tangible value at speed and scale. We are a talent- and innovation-led company with approximately 791,000 people serving clients in more than 120 countries. Technology is at the core of change today, and we are one of the world’s leaders in helping drive that change, with strong ecosystem relationships. We combine our strength in technology and leadership in cloud, data and AI with unmatched industry experience, functional expertise and global delivery capability. Our broad range of services, solutions and assets across Strategy & Consulting, Technology, Operations, Industry X and Song, together with our culture of shared success and commitment to creating 360° value, enable us to help our clients reinvent and build trusted, lasting relationships. We measure our success by the 360° value we create for our clients, each other, our shareholders, partners and communities. Visit us at accenture.com
CEOs call for a new era of pragmatic execution that embeds sustainability in strategy and culture (96%), but warn of capability gaps in technology and communications.
NEW YORK, Sept. 16, 2025 /PRNewswire/ — United Nations — CEOs shift from ambition to activation on sustainability, with nearly all (99%) stating their intent to maintain or expand their commitments, according to the 2025 edition of the CEO Study from the United Nations Global Compact and Accenture. Despite only a small percentage (fewer than 15%) feeling well prepared for major global challenges, including inflation, trade and climate change, a majority (88%) of CEOs say the business case for sustainability is stronger than it was five years ago.
Unlocking the Next Era of Sustainability Leadership
“Turning the Key: Unlocking the Next Era of Sustainability Leadership” comes at a critical time, as 2024 marks the first calendar year to exceed the Paris Agreement’s 1.5°C threshold. The report offers one of the most comprehensive longitudinal views of CEO sentiment on sustainability, published as the UN Global Compact celebrates its 25th anniversary.
Commenting on the study’s findings, Sanda Ojiambo, CEO and Executive Director of the UN Global Compact said: “CEOs are crystal clear: sustainability has moved from moral imperative to business fundamental. This study sets out a pragmatic playbook: work with regulators, meet fast-rising consumer expectations, invest in technology and skills, and communicate progress credibly. As the world breached the 1.5°C threshold and with a $4.3 trillion annual SDG financing gap leaving 3.4 billion people in countries spending more on interest than on health or education, the private sector must close the execution gap—embedding sustainability into strategy and culture, scaling innovation across value chains, and partnering to shape rules that reward long-term business value. Companies that act on these findings will build resilience, unlock growth, grow industries, stimulate economies and accelerate delivery of the Sustainable Development Goals.”
The 2025 CEO Study distills five “keys” to unlock momentum at scale: collaborate on regulation; harness consumer demand; expand access to technology; upskill for the future; and lead with credibility and purpose. CEOs are already preparing for a more regulated future—92% say strong global governance and unified policy are important or critical; 95% report regulatory compliance is a leading organizational priority; and 84% believe their companies are ready to meet upcoming sustainability regulations.
At the same time, consumer influence is gaining ground, alongside that of governments, employees and even investors. Ninety-eight per cent agree the private sector can drive progress through sustainable products and services, and 96% of CEOs advise their successors to embed sustainability in the company vision and culture. But gaps persist, particularly around digital tools to track and measure sustainability performance across value chains, which can limit how fully companies are able to respond to rising demand.
The report further finds that governance and technology-based skills for forward-looking risk capabilities are also lagging: only one in four (26%) CEOs report having dedicated scenario-planning teams and even less (fewer than 15%) feel well-prepared for major macroeconomic and sustainability challenges. And while 96% of CEOs say innovation and technology are essential to achieving global sustainability goals, 27% are considering leveraging digital tools for sustainability tracking and measurement.
“Business leaders know that technology, data and AI are critical to meeting their sustainability targets, yet gaps persist as they move from ambition to execution,” said Stephanie Jamison, Global Resources Industry Practice Chair and Global Sustainability Services Lead at Accenture. “Across industries and geographies, our clients are eager to move away from isolated projects toward adopting a multigenerational approach that compounds learnings, accelerates delivery and reduces cost. This can be a blueprint for growth that pairs sustainability commitments with bold, AI-driven reinvention that is built-in, not bolted on.”
Notes to Editors
About the CEO Study Program The CEO Study Program, developed by the UN Global Compact in collaboration with Accenture, is one of the largest global studies of CEO sentiment on sustainability. Through a quantitative assessment of nearly 2,000 CEOs and in-depth one-to-one interviews with CEOs, chairpersons and presidents of UN Global Compact member companies, this research coalesces perspectives to analyze key developments and emerging trends in sustainability. The CEO Study report is an extensive review of the advancing corporate sustainability movement aimed at accelerating progress for the UN Sustainable Development Goals.
About the UN Global Compact The ambition of the UN Global Compact is to accelerate and scale the global collective impact of business by upholding the Ten Principles and delivering the SDGs through accountable companies and ecosystems that enable change. With more than 20,000 participating companies, 5 Regional Hubs, 64 Country Networks covering 85 countries and 9 Country Managers establishing Networks in 16 other countries, the UN Global Compact is the world’s largest corporate sustainability initiative—one Global Compact uniting business for a better world. For more information, follow @globalcompact on social media and visit our website at unglobalcompact.org.
About Accenture Accenture is a leading global professional services company that helps the world’s leading businesses, governments and other organizations build their digital core, optimize their operations, accelerate revenue growth and enhance citizen services—creating tangible value at speed and scale. We are a talent- and innovation-led company with approximately 791,000 people serving clients in more than 120 countries. Technology is at the core of change today, and we are one of the world’s leaders in helping drive that change, with strong ecosystem relationships. We combine our strength in technology and leadership in cloud, data and AI with unmatched industry experience, functional expertise and global delivery capability. Our broad range of services, solutions and assets across Strategy & Consulting, Technology, Operations, Industry X and Song, together with our culture of shared success and commitment to creating 360° value, enable us to help our clients reinvent and build trusted, lasting relationships. We measure our success by the 360° value we create for our clients, each other, our shareholders, partners and communities. Visit us at accenture.com.
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The ground-shaking that an earthquake generates is only a fraction of the total energy that a quake releases. A quake can also generate a flash of heat, along with a domino-like fracturing of underground rocks. But exactly how much energy goes into each of these three processes is exceedingly difficult, if not impossible, to measure in the field.
Now MIT geologists have traced the energy that is released by “lab quakes” — miniature analogs of natural earthquakes that are carefully triggered in a controlled laboratory setting. For the first time, they have quantified the complete energy budget of such quakes, in terms of the fraction of energy that goes into heat, shaking, and fracturing.
They found that only about 10 percent of a lab quake’s energy causes physical shaking. An even smaller fraction — less than 1 percent — goes into breaking up rock and creating new surfaces. The overwhelming portion of a quake’s energy — on average 80 percent — goes into heating up the immediate region around a quake’s epicenter. In fact, the researchers observed that a lab quake can produce a temperature spike hot enough to melt surrounding material and turn it briefly into liquid melt.
The geologists also found that a quake’s energy budget depends on a region’s deformation history — the degree to which rocks have been shifted and disturbed by previous tectonic motions. The fractions of quake energy that produce heat, shaking, and rock fracturing can shift depending on what the region has experienced in the past.
“The deformation history — essentially what the rock remembers — really influences how destructive an earthquake could be,” says Daniel Ortega-Arroyo, a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS). “That history affects a lot of the material properties in the rock, and it dictates to some degree how it is going to slip.”
The team’s lab quakes are a simplified analog of what occurs during a natural earthquake. Down the road, their results could help seismologists predict the likelihood of earthquakes in regions that are prone to seismic events. For instance, if scientists have an idea of how much shaking a quake generated in the past, they might be able to estimate the degree to which the quake’s energy also affected rocks deep underground by melting or breaking them apart. This in turn could reveal how much more or less vulnerable the region is to future quakes.
“We could never reproduce the complexity of the Earth, so we have to isolate the physics of what is happening, in these lab quakes,” says Matěj Peč, associate professor of geophysics at MIT. “We hope to understand these processes and try to extrapolate them to nature.”
Peč (pronounced “Peck”) and Ortega-Arroyo reported their results on Aug. 28 in the journal AGU Advances. Their MIT co-authors are Hoagy O’Ghaffari and Camilla Cattania, along with Zheng Gong and Roger Fu at Harvard University and Markus Ohl and Oliver Plümper at Utrecht University in the Netherlands.
Under the surface
Earthquakes are driven by energy that is stored up in rocks over millions of years. As tectonic plates slowly grind against each other, stress accumulates through the crust. When rocks are pushed past their material strength, they can suddenly slip along a narrow zone, creating a geologic fault. As rocks slip on either side of the fault, they produce seismic waves that ripple outward and upward.
We perceive an earthquake’s energy mainly in the form of ground shaking, which can be measured using seismometers and other ground-based instruments. But the other two major forms of a quake’s energy — heat and underground fracturing — are largely inaccessible with current technologies.
“Unlike the weather, where we can see daily patterns and measure a number of pertinent variables, it’s very hard to do that very deep in the Earth,” Ortega-Arroyo says. “We don’t know what’s happening to the rocks themselves, and the timescales over which earthquakes repeat within a fault zone are on the century-to-millenia timescales, making any sort of actionable forecast challenging.”
To get an idea of how an earthquake’s energy is partitioned, and how that energy budget might affect a region’s seismic risk, he and Peč went into the lab. Over the last seven years, Peč’s group at MIT has developed methods and instrumentation to simulate seismic events, at the microscale, in an effort to understand how earthquakes at the macroscale may play out.
“We are focusing on what’s happening on a really small scale, where we can control many aspects of failure and try to understand it before we can do any scaling to nature,” Ortega-Arroyo says.
Microshakes
For their new study, the team generated miniature lab quakes that simulate a seismic slipping of rocks along a fault zone. They worked with small samples of granite, which are representative of rocks in the seismogenic layer — the geologic region in the continental crust where earthquakes typically originate. They ground up the granite into a fine powder and mixed the crushed granite with a much finer powder of magnetic particles, which they used as a sort of internal temperature gauge. (A particle’s magnetic field strength will change in response to a fluctuation in temperature.)
The researchers placed samples of the powdered granite — each about 10 square millimeters and 1 millimeter thin — between two small pistons and wrapped the ensemble in a gold jacket. They then applied a strong magnetic field to orient the powder’s magnetic particles in the same initial direction and to the same field strength. They reasoned that any change in the particles’ orientation and field strength afterward should be a sign of how much heat that region experienced as a result of any seismic event.
Once samples were prepared, the team placed them one at a time into a custom-built apparatus that the researchers tuned to apply steadily increasing pressure, similar to the pressures that rocks experience in the Earth’s seismogenic layer, about 10 to 20 kilometers below the surface. They used custom-made piezoelectric sensors, developed by co-author O’Ghaffari, which they attached to either end of a sample to measure any shaking that occurred as they increased the stress on the sample.
They observed that at certain stresses, some samples slipped, producing a microscale seismic event similar to an earthquake. By analyzing the magnetic particles in the samples after the fact, they obtained an estimate of how much each sample was temporarily heated — a method developed in collaboration with Roger Fu’s lab at Harvard University. They also estimated the amount of shaking each sample experienced, using measurements from the piezoelectric sensor and numerical models. The researchers also examined each sample under the microscope, at different magnifications, to assess how the size of the granite grains changed — whether and how many grains broke into smaller pieces, for instance.
From all these measurements, the team was able to estimate each lab quake’s energy budget. On average, they found that about 80 percent of a quake’s energy goes into heat, while 10 percent generates shaking, and less than 1 percent goes into rock fracturing, or creating new, smaller particle surfaces.
“In some instances we saw that, close to the fault, the sample went from room temperature to 1,200 degrees Celsius in a matter of microseconds, and then immediately cooled down once the motion stopped,” Ortega-Arroyo says. “And in one sample, we saw the fault move by about 100 microns, which implies slip velocities essentially about 10 meters per second. It moves very fast, though it doesn’t last very long.”
The researchers suspect that similar processes play out in actual, kilometer-scale quakes.
“Our experiments offer an integrated approach that provides one of the most complete views of the physics of earthquake-like ruptures in rocks to date,” Peč says. “This will provide clues on how to improve our current earthquake models and natural hazard mitigation.”
This research was supported, in part, by the National Science Foundation.
