Science and sanctions: lessons learned from twelve years of collaboration with the DPRK (North Korea)

The use of international sanctions has increased dramatically since the end of the second World War (Figure 1) and these have become more complex due to their multinational nature when implemented through the United Nations or European Union. However, over this same period, science has become more international, with multinational collaborations becoming the norm. This apparent paradox of simultaneously restricting and encouraging international collaboration creates many challenges for scientists and gives rise to the following questions: How do international sanctions affect scientific collaboration? What are the most effective avenues to maintain scientific collaboration during times of geopolitical strain? This paper investigates the unintended impacts of sanctions on scientific collaboration based primarily on the author’s experiences of collaborative research at a time of sanction development and implementation in the Democratic People’s Republic of Korea (DPRK, the formal name for North Korea)

The Seismic Signature of Upper-Mantle Plumes: Application to the Northern East African Rift

Several seismic and numerical studies proposed that below, some hotspots upper-mantle plumelets rise from a thermal boundary layer below 660 km depth, fed by a deeper plume source.We recently found tomographic evidence of multiple upper-mantle upwellings, spaced by several 100 km, rising through the transition zone below the northern East African Rift. To better test this interpretation, we run 3-D numerical simulations of mantle convection for Newtonian and non-Newtonian rheologies, for both thermal instabilities rising from a lower boundary layer, and the destabilization of a thermal anomaly placed at the base of the box (700–800 km depth). The thermal structures are converted to seismic velocities using a thermodynamic approach. Resolution tests are then conducted for the same P and S data distribution and inversion parameters as our traveltime tomography. The Rayleigh Taylor models predict simultaneous plumelets in different stages of evolution rising from a hot layer located below the transition zone, resulting in seismic structure that looks more complex than the simple vertical cylinders that are often anticipated. From the wide selection of models tested, we find that the destabilization of a 200 ◦C, 100 km thick thermal anomaly with a non-Newtonian rheology, most closely matches the magnitude and the spatial and temporal distribution of the anomalies below the rift. Finally, we find that for reasonable upper-mantle viscosities, the synthetic plume structures are similar in scale and shape to the actual low-velocity anomalies, providing further support for the existence of upper-mantle plumelets below the northern East African Rift

Uppermost mantle (Pn) velocity model for the Afar region, Ethiopia: an insight into rifting processes

The Afar Depression, Ethiopia, offers unique opportunities to study the transition from continental rifting to oceanic spreading because the process is occurring onland. Using traveltime tomography and data from a temporary seismic deployment, we describe the first regional study of uppermost mantle P-wave velocities (VPn). We find two separate low VPn zones (as low as 7.2 km s−1) beneath regions of localized thinned crust in northern Afar, indicating the existence of high temperatures and, potentially, partial melt. The zones are beneath and off-axis from, contemporary crustal magma intrusions in active magmatic segments, the Dabbahu-Manda-Hararo and Erta'Ale segments. This suggests that these intrusions can be fed by off-axis delivery of melt in the uppermost mantle and that discrete areas of mantle upwelling and partial melting, thought to characterize segmentation of the uppermost mantle at seafloor spreading centres, are initiated during the final stages of break-up

Distribution of partial melt beneath Changbaishan/Paektu volcano, China/Democratic People's Republic of Korea

Changbaishan/Paektu volcano straddles the border between the Democratic People's Republic of Korea (DPRK) and China. It was responsible for one of the largest eruptions in history, the `Millennium Eruption' of 946 CE. An episode of unrest between 2002 and 2005, characterized by ination and seismicity, refocused attention on this volcano. While satellite remote sensing has provided synoptic observations, ground based surveillance has hitherto supported only disparate analyses and geophysical interpretations on either side of the border. Here, we derive receiver functions using seismic records from both DPRK and China. H–к stacking indicates thick crust (up to 40 km) and high average crustal VP/VS (up to 1.93) beneath the volcano. Grid search inversions constrain a signi_cant velocity reduction at ~7km depth and harmonic analysis suggests this dips away from the volcano, with shallowest depths centred beneath the volcano. Common conversion point migrations show that this anomaly extends ~30km from the volcano summit and possibly as far as neighbouring volcanoes. The co‐location of the velocity reduction with a zone of high conductivity, low velocity, low density material at the depth of the ination source implicated in the 2002‐2005 unrest, indicates that partial melt is present directly beneath Changbaishan/Paektu, likely recharged during the episode of unrest. Our study highlights the importance of continued surveillance of the volcano and the need for further geophysical studies to constrain more fully the triggers for unrest and controls on its evolution

Seismic evidence for a mantle transition zone origin of the Wudalianchi and Halaha volcanoes in Northeast China

There exists much debate about origins of cretaceous-present volcanism in northeast (NE) China. Here we present high-resolution seismic images of the upper mantle beneath NE China by inverting P-wave travel-time data recorded by two dense linear arrays. The inclusion of the new data set has greatly improved sampling of the upper mantle beneath the study region, providing tight constraint on the seismic structure under the intraplate Wudalianchi and Halaha volcanoes. Local-scale low P-wave velocity (low-Vp) anomalies are revealed in the shallow mantle beneath the two volcanoes, whereas a large-scale high-Vp zone is imaged in the mantle transition zone (MTZ). These new results suggest that the two volcanoes, though located at different sites above the stagnant Pacific slab in the MTZ, are likely related to the deep subduction and dehydration of the Pacific slab, possibly through hot and wet upwellings in the big mantle wedge (BMW) beneath Wudalianchi and through deeper hydrous upwelling related to slab avalanche beneath Halaha. Our results also reveal other striking features, such as high-Vp structures resting atop the 410 km discontinuity beneath the Great Xing’an Range and the Songliao Basin, which are attributed to detached continental lithosphere. The delamination most likely occurred in the Cretaceous, which induced widespread magmatism in NE China

A little data goes a long way: automating seismic phase arrival picking at Nabro Volcano with transfer learning

Supervised deep learning models have become a popular choice for seismic phase arrival detection. However, they do not always perform well on out-of-distribution data and require large training sets to aid generalization and prevent overfitting. This can present issues when using these models in new monitoring settings. In this work, we develop a deep learning model for automating phase arrival detection at Nabro volcano using a limited amount of training data (2,498 event waveforms recorded over 35 days) through a process known as transfer learning. We use the feature extraction layers of an existing, extensively trained seismic phase picking model to form the base of a new all-convolutional model, which we call U-GPD. We demonstrate that transfer learning reduces overfitting and model error relative to training the same model from scratch, particularly for small training sets (e.g., 500 waveforms). The new U-GPD model achieves greater classification accuracy and smaller arrival time residuals than off-the-shelf applications of two existing, extensively-trained baseline models for a test set of 800 event and noise waveforms from Nabro volcano. When applied to 14 months of continuous Nabro data, the new U-GPD model detects 31,387 events with at least four P-wave arrivals and one S-wave arrival, which is more than the original base model (26,808 events) and our existing manual catalog (2,926 events), with smaller location errors. The new model is also more efficient when applied as a sliding window, processing 14 months of data from seven stations in less than 4 h on a single graphics processing unit

The future of passive seismic acquisition

It is an exciting time to be a seismologist. In November 2018, the InSight lander touched down on Mars and the first seismometer was deployed on another planet. This incredible feat means planetary seismologists are currently searching for marsquakes and will hopefully soon be providing images of its interior and helping us to understand how rocky planets form. However, we have been doing this for a long time in more familiar territory back home on Earth, where the field of terrestrial seismology has reached a turning point with significant developments in instrumentation and the manner of their deployment in recent years. However, equipment available to the UK community has not kept pace and needs urgent regeneration if the UK is to lead in the field of passive seismology in the future. To begin the process of redesigning the UK’s equipment for the next few decades, the British Geophysical Association sponsored a meeting in Edinburgh in late 2018 to discuss the future of passive seismic acquisition. What follows is a historical account of how and why we arrived at the present day UK seismological research and resource base, a summary of the Edinburgh meeting, and a vision for the passive seismic facilities required to support the next 20 years of seismological research

Upper mantle temperature and the onset of extension and break-up in Afar, Africa

It is debated to what extent mantle plumes play a role in continental rifting and eventual break-up. Afar lies at the northern end of the largest and most active present-day continental rift, where the East African Rift forms a triple junction with the Red Sea and Gulf of Aden rifts. It has a history of plume activity yet recent studies have reached conflicting conclusions on whether a plume still contributes to current Afar tectonics. A geochemical study concluded that Afar is a mature hot rift with 80 km thick lithosphere, while seismic data have been interpreted to reflect the structure of a young, oceanic rift basin above mantle of normal temperature. We develop a self-consistent forward model of mantle flow that incorporates melt generation and retention to test whether predictions of melt chemistry, melt volume and lithosphere–asthenosphere seismic structure can be reconciled with observations. The rare- earth element composition of mafic samples at the Erta Ale, Dabbahu and Asal magmatic segments can be used as both a thermometer and chronometer of the rifting process. Low seismic velocities require a lithosphere thinned to 50 km or less. A strong positive impedance contrast at 50 to 70 km below the rift seems linked to the melt zone, but is not reproduced by isotropic seismic velocity alone. Combined, the simplest interpretation is that mantle temperature below Afar is still elevated at 1450◦C, rifting started around 22–23 Ma, and the lithosphere has thinned from 100 to 50 km to allow significant decompressional melting

Initiation of a proto‐transform fault prior to seafloor spreading

Transform faults are a fundamental tenet of plate tectonics, connecting offset extensional segments of mid‐ocean ridges in ocean basins worldwide. The current consensus is that oceanic transform faults initiate after the onset of seafloor spreading. However, this inference has been difficult to test given the lack of direct observations of transform fault formation. Here, we integrate evidence from surface faults, geodetic measurements, local seismicity, and numerical modelling of the subaerial Afar continental rift and show that a proto‐transform fault is initiating during the final stages of continental breakup. This is the first direct observation of proto‐transform fault initiation in a continental rift, and sheds unprecedented light on their formation mechanisms. We demonstrate that they can initiate during late‐stage continental rifting, earlier in the rifting cycle than previously thought. Future studies of volcanic rifted margins cannot assume that oceanic transform faults initiated after the onset of seafloor spreading