Carbon Chemist

Tag: Seismology

  • I work to protect South Korea’s people against earthquakes

    I work to protect South Korea’s people against earthquakes

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    “In this photo, I’m examining a previously hidden active fault line between two geological blocks. I discovered it with other researchers working for the Korea Active Fault Research Group (KAFRG). The site is on a ridge in a forested valley about an hour’s drive from my office at Kyungpook National University in Daegu, South Korea. It’s part of the Hwalseongri fault, situated just south of Gyeongju National Park.

    In 2016 and 2017, large earthquakes occurred in this area, causing great concern in our country. Until the Tōhoku earthquake in 2011 caused the nuclear disaster at Fukushima in nearby Japan, people in South Korea had not paid much attention to active faults. We’ve become more worried about seismic risks since then.

    In 2017, South Korea’s government founded KAFRG to create the country’s first active-fault map. I’m one of around 60 scientists working as part of the group, which is based at Pukyong National University in Busan. My mission is to identify active faults that have the potential to cause earthquakes.

    To do this, I collect evidence known as geomorphic markers. My tasks include analysing such linear features, together with fault-related landforms and the structural correlation of faults. Using the information I provide, geologists and geophysicists can conduct more detailed studies of these faults.

    My fieldwork for KAFRG often uses drones to look for fault lines. However, for land covered by forest, lidar (laser imaging detection and ranging) technology is more important. Our research team uses aircraft to obtain lidar data for the areas we need to study. But because geomorphic markers are often hard to find, we also need to walk through forests and cross rivers. The best tool of all is my feet.”

    This interview has been edited for length and clarity.

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  • Weird signal that baffled seismologists traced to mega-landslide in Greenland

    Weird signal that baffled seismologists traced to mega-landslide in Greenland

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    Front view of the terminus of Hisinger Glacier at the Dickson Fjord in the Northeast Greenland National Park.

    Greenland’s Dickson Fjord, where last year a 1.2-kilometre-high mountain peak collapsed into the fjord triggering a far-reaching seismic signal.Credit: Jane Rix/Alamy

    On 16 September 2023, seismologists worldwide registered a weird signal emanating from eastern Greenland. Missing were the variations in frequency that typically accompany events such as earthquakes: the signal was ‘monochromatic’, resembling the ringing of a bell, and lasted nine days. It was quickly registered as a UFO, er, USO: an unidentified seismic object.

    “It’s the first time we’ve found a seismic signal of this type in the global record: some people thought their sensors were broken,” says Kristian Svennevig, a geologist at the Geological Survey of Denmark and Greenland in Copenhagen, who led a study1 of the event, published on 12 September in Science. Far-flung stations registered the signal, including one halfway around the globe in Antarctica.

    Reports of a tsunami at a research station in Greenland’s Dickson Fjord arrived at around the same time, and scientists pinpointed the likely source: a 1.2-kilometre-high mountain peak had collapsed into a gully in the fjord. They now had a culprit, but it remained unclear how a landslide could produce such a long-lasting reverberation. Svennevig and his colleagues assembled an interdisciplinary team to investigate.

    Precedents for such seismological signals existed in the scientific literature going back more than a decade. Landslides in closed water basins had produced a back-and-forth sloshing motion, known as a seiche, yielding a monochromatic seismic signature similar to the 2023 one. The difference was that these events were registered only locally and lasted less than an hour.

    Sloshing motion

    Svennevig and his colleagues began documenting the landslide and the resulting tsunami. They calculated that the collapse of the mountain top produced a landslide carrying some 25 million cubic metres of material, equivalent to roughly 10,000 Olympic swimming pools. The earthen material smashed into a local glacier at the bottom of a gully, creating a rock–ice avalanche that cascaded sidelong into the fjord.

    The initial splash was 200 metres tall, with subsequent waves roughly half that height, Svennevig says. The tsunami was still 4 metres high some 75 kilometres from the initial impact. But what made the event unique was the apparent persistence of the sloshing motion — with waves of roughly 7 metres — that continued between the mountainous sides of the narrow fjord. Using detailed military maps of the floor of the fjord, the team modelled the event, suggesting that the landslide could have produced the mysterious signal.

    It’s a nice study that explains an “extremely weird and unusual” seismological event, says Göran Ekström, a geophysicist at the Columbia University’s Lamont-Doherty Earth Observatory in Palisades, New York. He chalks it up to teamwork and the sharing of data. “The speed at which the team was able to document, describe and explain the sequence of events shows how science can work these days.”

    In the end, Svennevig and his team suggests that the actual culprit was global warming, which thinned the glacier underpinning the mountain and ultimately set the stage for the landslide. “We will probably see more of these funky events in the future,” he says.

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  • Highly variable magmatic accretion at the ultraslow-spreading Gakkel Ridge

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  • These labs have prepared for a big earthquake — will it be enough?

    These labs have prepared for a big earthquake — will it be enough?

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    Earlier this month, Japan’s Meteorological Agency issued its first-ever ‘megaquake’ alert, advising that the risk of a large earthquake along the Pacific coast was higher than usual. The warning came after an earthquake with a magnitude of 7.1 on 8 August.

    The agency lifted the warning a week later, after no major change in seismic activity was detected. But the alert was another reminder for scientists who live in Japan and other seismic zones of the constant threat that an earthquake could disrupt — or even destroy — their research. So how do they safeguard their laboratories? Nature spoke to seven researchers about their preparations and whether those are enough.

    Securing equipment

    When the Tōhoku earthquake and tsunami hit in March 2011, Masahiro Terada, an organic chemist at Tohoku University in Sendai, found broken glass scattered across his lab, fume hoods weighing 400 kilograms metres away from their usual position and water from broken pipes flooding the space. The smell of organic solvents filled the lab and a fire had broken out in the reagent storage room. Terada lost ten years’ worth of synthesized compounds.

    These days, Terada anchors large furniture and equipment directly to the concrete wall and stores reagents in cushioned mesh containers.

    Each year, biochemist Hideki Tatsukawa is securing more and more of his lab’s equipment at Nagoya University, under the institute’s guidance. The university is located in a region that has a more than 70% likelihood of a severe earthquake in the next 30 years, according to the Japanese government. Tatsukawa anchors any equipment taller than one metre, such as refrigerators, with vertical bands to the floor to prevent them from toppling or jumping during a quake.

    Tying down equipment is crucial for saving lives and preventing secondary disasters, such as broken gas pipes or exposed electrical wiring that could spark a fire, says Koji Fukuoka, a risk-management researcher formerly at Kyushu University in Fukuoka, Japan. Fires only take two minutes to reach the ceiling in most Japanese buildings, he says, so “removing potential causes of fire needs to be one of the top priorities in a lab setting”. Fukuoka recommends that labs have two evacuation routes in case one of them becomes compromised.

    Damage to equipment during earthquakes can also result in considerable financial losses. During the 2011 quake, damage to research instruments cost Tohoku University 26.9 billion yen (US$180 million). In the wake of that earthquake, the university established a Disaster Management Promotion Office, which issues technical guidelines on how to secure equipment depending which floor of the building they are on. For instance, nuclear magnetic resonance (NMR) spectroscopy instruments should be installed on the ground floor and on top of a base isolation stand, which isolates the equipment from the floor so that it moves independently of the shaking ground. NMR instruments can explode because of the helium liquid they contain becomes a gas when the equipment is broken and might deplete rooms of oxygen.

    “But, to our knowledge, these learnings haven’t been shared across universities systematically,” says Takeshi Sato, a disaster-prevention scientist at Tohoku University. Fukuoka also notes that, without expert advice and dissemination of knowledge, each lab’s precautions might not be enough in the event of very strong shaking.

    Backing up samples

    One of the main concerns for Kentaro Noma, a neurobiologist at Nagoya University, is losing the more than 600 unique strains of nematode worm (Caenorhabditis elegans) that he has produced over the course of his career so he could study the relationship between genetics and the ageing of neurons. “Losing the strains not only compromises my own work, but research reproducibility for the wider scientific community,” he says.

    In addition to the stocks that Noma currently uses for his research, he maintains two backup collections: one in a freezer cooled to −80 °C kept in his lab and another stored in liquid nitrogen, also in the lab. The freezer has a backup power generator that runs on gasoline; the collection stored in liquid nitrogen serves as an extra safeguard in case of an extreme disaster, when there is no access to fuel. “It’s not perfect, but the liquid-nitrogen freezer buys us an extra 1–2 weeks to devise longer-term measures,” he says.

    Tatsukawa, who studies the functions of proteins in model organisms, preserves genetically engineered lines of mice and medaka fish (Oryzias latipes) by extracting sperm, mixing the samples with a preservation solution and freezing them in liquid nitrogen. The cryogenically preserved samples can be thawed, and female animals can be artificially inseminated to restart the line.

    Similar precautions are being taken by scientists at the University of California in the San Francisco Bay Area, which sits directly on top of the Hayward Fault. There is a more than 30% chance of an earthquake with a magnitude of 6.7 or higher occurring on the fault iby 2043.

    Dirk Hockemeyer, a cell biologist at the University of California, Berkeley, also cryogenically preserves his stem-cell lines in liquid nitrogen, a standard procedure in his field. He has more than 25,000 vials of cell lines produced by the 50 researchers that have worked in his lab over the past 10 years. As a preventative measure, Hockemeyer keeps duplicates of valuable cell lines in liquid nitrogen in different buildings in case one collapses.

    Research animals

    For scientists who work with animals, there are many factors to consider in earthquake preparation. In Japan, facilities with primates typically have two-tiered walls so that if one layer is destroyed, the other keeps the animals contained, says Ikuma Adachi, a primatologist at Kyoto University in Inuyama. Kyoto University’s Center for Human Evolution Modeling Research houses 11 chimpanzees (Pan troglodytes) and 800 macaques (Macaca sp.). “Primates are very sensitive to changes in the environment and will become anxious during disasters,” he says. Securing water for them to drink and maintaining hygienic conditions for the animals to live in is also crucial, says Adachi.

    “The best we can do is to prepare measures and protocols in advance so that it guides decision-making during emotionally challenging times,” he says.

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  • Inner core backtracking by seismic waveform change reversals

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    The inner core (IC) has been known to change over decades since the discovery of changing seismograms of repeating earthquakes1,7. The dominant interpretation of steady super-rotation over decades has been derived from temporal changes of up to tenths of a second in the difference in arrival times between PKIKP and later core phases in repeated earthquakes. The inferred rate of super-rotation has settled to about 0.05–0.15° per year, and motion in the past decade may have slowed8,9,10. Similar rates have been inferred from normal modes11, PKIKP coda wave changes12, IC-backscattered waves2,13,14 and antipodal core waveform changes15. Fluctuating and much faster motion has also been suggested16. Most recently, observation with medium-aperture, high-frequency arrays and individual stations has suggested that PKIKP coda waves from 1991 to 2017 changed over time primarily during the interval 2001 to 2003, which is interpreted as because of 0.5° IC rotation during that period and much less rotation at other times17.

    Other studies suggest oscillating motion. The distinct six-year oscillation (SYO) in the length of day (LOD) could be explained by gravitational coupling of mantle density anomalies and core–mantle boundary topography with inner-core boundary (ICB) topography18,19, although alternate explanations have been proposed20,21,22. A reversal of motion inferred from backscattered seismic waves was consistent with the amplitude and phase predicted from the SYO pattern of LOD oscillation19,23.

    Apparent inconsistencies with the pattern expected from rotation in changes in PKIKP coda have been argued to preclude interpretation of solid-body IC rotation, and instead indicate structural changes in the IC or at the ICB, or conceivably in the outer core (OC)24,25,26.

    To resolve the inconsistency of recent models, here we gather and analyse additional data sensitive to IC changes. We focus on two short-period, medium-aperture seismic arrays in northern North America, the Eielson (ILAR) and Yellowknife (YKA) arrays, which record IC-sensitive PKIKP waves from earthquakes in the South Sandwich Islands (SSI). We compile repeating earthquakes from the literature for 1991–2020, and crucially add 12 new repeating earthquakes for 2021–2023. We carefully examine the seismograms for changes in PKIKP and its coda. The dependence of waveform changes on earthquake pair dates is used to construct a new model for IC rotation.

    We collected a dense sampling of repeating earthquakes (Fig. 1b). We focus on the region in which IC change was first noted5, and which has clear waveform changes and changes in the time difference between core phases (ddt) over more than 50  years (ref. 27)—the path from the SSI to northern North America (Fig. 1a). This path is close to north–south, a bearing shown to be most likely to reveal waveform changes from IC rotation17. Beamforming greatly improves the signal-to-noise ratio, so we select the high-quality, 20-element ILAR and YKA arrays, which have been recorded for more than 20 years. They were designed with apertures and siting appropriate for capturing clear teleseismic P waves at periods near 1 s.

    Fig. 1: Seismic ray paths and event locations.
    figure 1

    a, Ray paths of PKIKP and PKP from the SSI source region to the two arrays (ILAR and YKA). The sampled IC region with a representative 1.5 Hz Fresnel zone30 is marked with dashed circles centred at the PKIKP pierce points at the ICB. Inset, the ray paths of PKP (PKP(AB) and PKP(BC)), PKiKP(CD) and PKIKP(DF). b, Map of the SSI region with the source locations coloured by focal depth.

    We compile 121 events from 1991 to 2023 (Supplementary Table 1) in 42 locations, including 16 multiplets (Supplementary Table 2) of three to seven events, which span 5° in latitude. The latest 12 events were found with a template search (Methods). These earthquakes form 143 pairs of repeating events (Supplementary Table 3). Between the two arrays, we made 200 waveform pair comparisons. The comparisons were done with stacks across each array (Methods).

    Many PKIKP waves showed changes over the years, whereas we noticed no evidence that non-PKIKP phases changed in either arrival time or waveform, including IC-reflected phases. Many examples of these event pairs with changing waveforms have been presented in ref. 17.

    We scored PKIKP by visual inspection for all event pairs from both arrays, classifying the waveform match as similar, somewhat similar or different, resulting in 57, 72 and 71 pairs, respectively. There were also 48 pairs too noisy to evaluate and 38 for which data from ILAR, which has the shorter archive, were not available. Almost all of our scores match the interpretation in ref. 17 for the presence or absence of waveform change. More objective scoring is possible17, but some level of subjectivity would remain. Noise level, the time interval that the DF phase is above the noise, amplitude relative to nearby reference phases, character of other nearby repeating pairs and repeater similarity on global stations for non-IC phases all were evaluated, as well as potential differences between repeats in location and source time function. A further complication is that ILAR at 150° and YKA at 135° present PKP waves with distinct patterns of timing and amplitude of PKIKP and PKiKP, and interference with other core phases. The pattern and model described below become clear, in our opinion, and the model predictions should be testable within the next 5–10 years.

    Figure 2 shows two examples of a triplet of event pairs constructed from two three-event multiplets. The middle-event waveform differs from those of the first and last events, which are essentially identical in each case. That is, remarkably, the PKIKP changes then reverts to the original across the three events. One or two such instances could simply indicate that the middle event is anomalous in a variety of possible ways, so we investigate more thoroughly.

    Fig. 2: Waveform comparison of multiplets.
    figure 2

    a, The triplet that forms multiplet O, which repeats in 2003, 2009 and 2020. b, The triplet that forms multiplet J, which repeats in 2002, 2009 and 2022.

    The very similar initial first few seconds of most of the repeating-event waveforms is the expected result of scattering in a heterogeneous medium that has shifted. Waveform changes become greater with increasing lag time behind the direct arrival, as was demonstrated by synthetic seismograms in ref. 17.

    The results for both arrays for all events, and just the 96 most similar events, are shown in Extended Data Figs. 1–4. Some broad patterns are evident. Pairs in the south show less difference at YKA. Most pairs that start in the early years change waveform. Note that there are fewer pairs for ILAR because of its later starting date for data availability from Incorporated Research Institutions for Seismology (IRIS). These observations are hard to translate into IC motion as plotted.

    Notably, some widely separated pairs of events happen with unchanged waveforms, as noted in ref. 17. Even more surprising is that five or so multiplets, spread across the SSI region, change waveform and then change back across a span of a decade or more, as shown in Fig. 2.

    We interpret below that these observations indicate a reversing IC that shifts first in one direction and then back to reoccupy the same position. Further examples of waveforms changing and reverting are shown in Extended Data Fig. 5. In this model, any event pair with matching waveforms at long intervals may well have produced different waveforms if a repeater had ruptured at times in between. Other pairs are similar but change in different pairings from the same multiplet with later or earlier times, as shown in Extended Data Fig. 6, and still others are simply pairs many years apart showing little change in SSI regions in which differently timed pairs generally do show a change. Southern SSI shows strong direct arrivals with weak scattered coda, with all changes more subtle, so we interpret waveform changes that are more subtle, notably in multiplets A and C. Scored changes for multiplet A are shown in Extended Data Fig. 7.

    To investigate this model, we consider the dates of pairs with similar and different waveforms against their time separation. The matching pairs of times reveal when a rotation angle is repeated. In the context of previous models, which mostly find super-rotation in our early time span, probably the first repetition in matching repeaters is when the IC is super-rotating, and the later repetition is passing back through that same position while sub-rotating. The model and measurement are shown in Fig. 3.

    Fig. 3: Schematic of rotation observations.
    figure 3

    a, Diagram showing the relation between rotation angle and recurrence interval at times A, B and C during reversal of differential rotation. b,c, Rotation angle (b) and recurrence interval (c) at times A, B and C during reversal of differential rotation.

    The degree of similarity of the waveforms traversing the IC for all 143 most similar event pairs is shown in Fig. 4. The similar pairs tend to have their midpoint around 2010, with longer intervals of 15–20 years between events that extend farther from 2010, earlier for the first event and later for the second event. This is the pattern expected for an IC that has reversed direction near the date of the midpoint.

    Fig. 4: Dates of similar (red), somewhat similar (blue) and different (green) pairs of repeating events.
    figure 4

    The dots are the years of events, the lines connect repeating pairs. The black line on the left shows that the trend of first events in a pair that has progressively shorter intervals occurs progressively later from 2000 to 2005. The black line on the right shows that the second event in a pair that has progressively longer intervals occurs progressively later from 2010 to 2023. Pairs less than 10 years apart are shaded, as just a few years of separation throughout the entire period apparently does not involve enough IC motion to always change the waveform. Lines from the ILAR array pair measurements are raised 0.4 years to visually separate them from the lines from the YKA array for the same event pairs.

    The pattern for all pairs, including the short recurrence times, showing which pairs do and do not fit this pattern, is shown differently in Extended Data Fig. 8. It is even more apparent there that for the matching pairs for longer intervals, the prediction in Fig. 3 matches closely the observations.

    The shallower slope after 2010 in Fig. 4 indicates slower motion than before 2005, and projects to a reversal occurring in 2008 (Methods). We cannot resolve absolute rotation rate from this plot alone, the plot only measures the polarity and rate ratio between forward and backward rotations. Only asymmetry in rate across the time of reversal can generate the observed change in slopes.

    The steeper slope before 2005 compared with that after 2015 shows that the IC motion is 2.5 times slower in the later period, as well as reversed (Methods). The IC motion has thus been more complicated than a symmetric function such as a sinusoid. We cannot trace motion back before about 2002—we see no waveform matches with events then, probably because the IC has not yet sub-rotated back to those positions.

    The period between 2005 and 2015 is more difficult to resolve. We interpret that the rotation in this period slows as the IC position reaches an extremum before reversing. The time near the change in direction produces a less definitive pattern of matches and mismatches, as slowing apparently lengthens the time interval over which the IC position remains similar. Waveforms across short intervals sometimes match even far from the turning point, also probably owing to only small changes in IC position.

    There may be signs of more activity apart from just IC rotation; some pairs that the model predicts to match do not. More might be learnt from measuring time shifts in the changing waveforms and perhaps beamforming to locate and analyse individual scatterers that evolve between repetitions. Initial examination, not shown, suggests that ILAR ddt measurements do change and then revert in phase with waveforms. Here we simply present IC rotation with repeated waveforms and do not explore the pairs that should match but do not.

    An IC that moves in one direction from 2002 to 2005, may not move much for a few years, then slowly backtracks from 2015 to 2023, resembles in broad form the recent years of motion in the model in ref. 27, which postulates a 70-year sinusoid slowing to reverse around 2010. Our measurements confirm the general trend, which had been controversial, and extend the observation period several more years, confirm a reversal and show asymmetry that had been not so clearly resolved. We verify for the first time that the path returns along a similar trajectory, without much wobble in the relative rotation pole.

    Our model does not provide a strong test of the model in ref. 17, which suggests an earlier period of more rapid IC motion from 2001 to 2003, preceded and followed by much less motion. Here we see, however, that slow motion persists through most years since and measure its trend and relative speed. Repeating events for these and other source-station paths may well in future years start to match waveforms from still earlier times, elucidating the movement that generated the strong changes in waveforms that our study and ref. 17 observed for repeating pairs crossing the 2001–2003 window.

    Our data do not resolve changes at the IC boundary or in the OC26; the PKPBC/CD arrivals do not change noticeably in waveform or timing. However, some earthquake pairs change when little is predicted from rotation and changes are seen when PKIKP and PKiKP overlap, allowing more IC variability than just rotation.

    Our observations do not detect our previously favoured model of the mantle–IC gravitational coupling driving SYOs as the primary IC motion23. We note that the inferred change in polarity around 1971 (ref. 23), which is consistent with SYO predictions, is also consistent with the expected timing of an inferred previous reversal in the slow oscillation model27 and a more variable rotation model28. We also note that improved estimates of the magnitude of IC motion necessary to cause the observed LOD oscillations include the likely entrainment of the OC in the tangent cylinder29. This additional inertial mass would reduce by a factor of two or three the angular amplitude of oscillation that would explain the SYOs in LOD, rendering it difficult to seismologically observe.

    Our method and observations provide the most definitive evidence so far that the IC is moving relative to the rest of the Earth, and specifically that it is slowly and smoothly rotating on a reversing path. The observation that the westward sub-rotation is less than half as fast as the last part of the eastward super-rotation is well-resolved and begs models with that character. Identification of repeating pairs in which waveform changes and ddt from rotation cancel will allow greater resolution in the question of whether other processes near the IC boundary are also appearing. Examination with these methods of repeating IC waves on other paths, further in the past and into the future, promises rapid progress in monitoring motion in a difficult and enigmatic region.

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  • Fault-network geometry influences earthquake frictional behaviour

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  • Seismological evidence for a multifault network at the subduction interface

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  • Taiwan hit by biggest earthquake in 25 years: why scientists weren’t surprised

    Taiwan hit by biggest earthquake in 25 years: why scientists weren’t surprised

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    Scientists warn that more shocks are likely after Taiwan was rocked by the most powerful earthquake to hit the island in 25 years, killing several people, flattening buildings, and triggering landslides. Geologists warn that the location of the epicentre is in a complex network of offshore faults, making aftershocks or even another quake a possibility.

    The magnitude-7.4 tremor struck under the ocean, 18 kilometres south of the east-coast city of Hualien just before 8am on Wednesday morning local time, according to measurements gathered by the US Geological Survey. Since then, dozens of aftershocks have rattled the island, including a 6.4 magnitude tremor that occurred roughly two hours after the main quake. “Everyone experienced the shaking,” says Kuo-Fong Ma, a seismologist at National Central University in Taoyuan City, Taiwan.

    The earthquake occurred at a relatively shallow 35 kilometres deep, resulting in stronger tremors than those produced by quakes that erupt farther below the Earth’s surface. Authorities issued tsunami warnings in Taiwan, Japan and the Philippines, though they later downgraded them. A 30-centimetre-high wave rolled into Yonaguni Island in the south of Japan about 15 minutes after the tremor. The earthquake’s effects were also reportedly felt in parts of mainland China.

    Taiwan’s vulnerability to earthquakes is no surprise given it is situated in one of the most seismically active regions in the world, says Meghan Miller, a seismologist at the Australian National University in Canberra. The east coast of the island sits on top of two converging tectonic plates: the Philippine Sea and Eurasian plates. Many of the earthquakes that occur on the eastern side of Taiwan are due to the Philippine Sea plate sliding underneath the Eurasian plate, says Miller.

    The location of the earthquake’s underwater epicentre offers clues to its mechanics, says Yu Wang, a geologist at National Taiwan University in Taipei. The earthquake occurred on a reverse fault, which means one chunk of rock shifted vertically relative to the other. “We believe this is the cause of the current earthquake,” says Wang. He adds that the area where the earthquake occurred contains a complex network of faults, and that the latest rupture probably produced a crack between 40 and 50 kilometres long.

    In the coming days, dozens of aftershocks are expected to shake Taiwan further, says Wang. The force of the earthquake has already triggered landslides in mountainous areas, which could worsen with more tremors and make rescue efforts more challenging, adds Miller. In flat areas, aftershocks could also lead to the ground becoming soft and water-logged, which can amplify seismic waves and damage compromised buildings further. “There can be additional damage on top of what originally occurred in the first event,” says Miller.

    Several earthquakes have occurred in Taiwan over the past century, with those reaching magnitude 7 usually occurring roughly every 30 years, says Ma. One of the most devastating earthquakes to hit the island occurred in 1999, when a magnitude-7.6 tremor struck the western side of the island. It resulted in more than 2,400 deaths and reduced thousands of buildings to rubble.

    But in the past two decades, Taiwan has ramped up its efforts to reduce the impact of earthquakes, says Ma. The island has an early warning system that alerts cities and regions via a telephone call a few seconds after an earthquake strikes. She adds that many buildings have been modified to withstand strong earthquakes, and several seismology stations have been installed across the island to take real-time measurements. Ma and her colleagues are also developing sensors for measuring the shaking intensity inside buildings to help people determine their risk during an earthquake. “I think that will be the future,” she says.

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  • Did ‘alien’ debris hit Earth? Startling claim sparks row at scientific meeting

    Did ‘alien’ debris hit Earth? Startling claim sparks row at scientific meeting

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    An electron microprobe image of a grey sphere on a black background. The sphere has a partially irregular surface and is about 200 micrometres across according to the scale bar.

    Avi Loeb and his team say that metallic balls found near Papua New Guinea could be of extraterrestrial origin.Credit: Avi Loeb’s photo collection

    The Woodlands, Texas

    A sensational claim made last year that an ‘alien’ meteorite hit Earth near Papua New Guinea in 2014 got its first in-person airing with the broader scientific community on 12 March. At the Lunar and Planetary Science Conference in The Woodlands, Texas, scientists clashed over whether a research team has indeed found fragments of a space rock that came from outside the Solar System.

    An ‘alien meteorite’ probably didn’t slam into Earth — how will we know if one does?

    The debate occurred at a packed session featuring Hairuo Fu, a graduate student at Harvard University in Cambridge, Massachusetts, who is a member of the team that found the fragments. Team leader Avi Loeb, an astrophysicist at Harvard who did not attend the conference, has made other controversial claims about extraterrestrial discoveries. Many scientists have said that they don’t want to spend much of their time analysing and refuting these claims.

    During his presentation, Fu described tiny metallic blobs that Loeb’s expedition dredged from the sea floor near Papua New Guinea last year, and said that the spherules have a chemical composition of unknown origin1. He then faced questions from a long line of scientists sceptical of the implications of extraterrestrial material. “At the very least, it is something different from what we know,” Fu responded.

    New work questions the team’s findings. In a manuscript posted on the arXiv preprint server on 8 March2, ahead of peer review, a researcher argues that the debris collected by Loeb and his co-workers is actually molten blobs generated when an asteroid hit Earth 788,000 years ago.

    “What they found has all the characteristics of microtektites — little pieces of melted Earth that came from this impact,” says preprint author Steve Desch, an astrophysicist at Arizona State University in Tempe.

    Meanwhile, other studies are challenging different aspects of Loeb’s claim, such as whether the meteor that reportedly produced the fragments was on the trajectory Loeb says it was. Together, the findings show how the broader scientific community is engaging with Loeb’s extraterrestrial claims, in spite of reluctance to do so.

    A unique find?

    ‘Interstellar’ objects remained in the realm of theory until 2017, when astronomers spotted the first known celestial object to be on a trajectory that meant it could only have come from outside the Solar System. Loeb made headlines when he speculated that the object, a comet-like body named ‘Oumuamua, was an artefact sent by an extraterrestrial civilization.

    ‘Oumuamua passed through the Solar System far from Earth, but Loeb hoped to find another interstellar object that had hit the planet. He later proposed that a bright meteor that appeared in the sky north of Papua New Guinea in January 2014 had an interstellar trajectory and could have scattered debris in the ocean.

    Three people use a vacuum tool on a metallic sledge on board a ship.

    Avi Loeb (in hat) and colleagues recover particles from a magnetic sledge on their 2023 expedition.Credit: Avi Loeb’s photo collection

    In June 2023, Loeb led a privately funded expedition to the site that used magnetic sledges to recover more than 800 metallic spherules from the sea floor. About one-quarter of the spherules had chemical compositions indicating that they came from igneous, or once-molten, rocks. Of those, a handful were unusually enriched in the elements beryllium, lanthanum and uranium. The researchers concluded that those spherules are unlike any known materials in the Solar System1.

    However, Desch counters that the spherules could have come from an asteroid impact in southeast Asia. Key to his proposal2 is a kind of soil called laterite, which forms in tropical regions when heavy rainfall carries some chemical elements from the topmost layers of soil into deeper ones. This leaves the upper soil enriched in other elements, including beryllium, lanthanum and uranium — similar to the composition of the spherules collected by Loeb and his colleagues. Desch says that an asteroid known to have struck the region around 788,000 years ago3 probably hit lateritic rock and created the molten blobs found by Loeb’s team.

    In an e-mail to Nature, Loeb argues that spherules from an impact 788,000 years ago should have been buried by ocean sediments. Desch counters that sedimentation rates are relatively low in the offshore area where the spherules were collected.

    But others are sceptical of Desch’s proposal, too. Scientists have yet to find any confirmed tektites from lateritic rock, notes Pierre Rochette, a geoscientist at Aix-Marseille University in Aix-en-Provence, France, who is not affiliated with either team. And very few tektites are magnetic, he says, so it would be difficult for Loeb and his colleagues to have pulled up hundreds from the sea floor.

    Fiery critiques

    Desch was not the only scientist to challenge Loeb’s work this week.

    How two intruders from interstellar space are upending astronomy

    After Fu’s conference presentation, Ben Fernando, a seismologist at Johns Hopkins University in Baltimore, Maryland, spoke and took aim at claims concerning the 2014 meteor. Fernando and his colleagues, including Desch, analysed seismic and acoustic data gathered by ground-based sensors at the time the meteor hit the atmosphere4. Data from a seismometer on nearby Manus Island, which Loeb and his team studied as they were deciding where to dredge, show no characteristics of a high-altitude fireball — but do indicate a vehicle driving past, Fernando said. “This is almost certainly a truck,” he told the meeting. A second set of observations, made using infrasound sensors that listen for clandestine nuclear tests, seems to have detected the meteor hitting the atmosphere, but suggests it happened around 170 kilometres away from where Loeb’s team calculates.

    Loeb told Nature that such critiques do not take into account US Department of Defense data that he says confirm the exact trajectory of that fireball. But because those data are held by the government, they have not been independently cross-checked by other scientists.

    As conference-goers poured out of the room after his talk, Fu told Nature that Loeb’s team is working on further analyses, such as isotopic studies, that could shed more light on what the spherules are. After that, Fu said, he is looking forward to graduating and working on a new project — on how the Moon was formed.

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