Exclusive Seismoacoustic Detection and Characterization of an Unseen and Unheard Fireball Over the North Atlantic

Small meteoroids that enter Earth's atmosphere often go unnoticed because their detection and characterization rely on human observations, introducing observational biases in space and time. Acoustic shockwaves from meteoroid ablation convert to infrasound and seismic energy, enabling fireball detection using seismoacoustic methods. We analyzed an unreported fireball in 2022 near the Azores, recorded by 26 seismometers and two infrasound arrays. Through polarization analyses, array methods, and 3‐D ray‐tracing, we determined that the terminal blast occurred at 40 km altitude, ∼60 km NE of São Miguel Island. This location matches an unidentified flash captured by a lightning detector aboard the GOES‐16 satellite. The estimated kinetic energy is ∼10−3 kT TNT equivalent, suggesting a 10−1 m object diameter, thousands of which enter the atmosphere annually. Our results demonstrate how geophysical methods, in tandem with satellite data, can significantly improve the observational completeness of meteoroids, advancing our understanding of their sources and entry processes

Crustal Structure of Prydz Bay at 72°E, East Antarctica

One-hundred-eighty million years ago the Gondwana super-continent broke apart into the continents of Antarctica, Africa, Australia, India and South America. Their drift created the present-day Indian and South Atlantic Ocean. When tectonic plates move apart, the continental drift causes the continental crust to extend until oceanic crust is created by seafloor spreading. This type of process can be observed in several places around the world, e.g. at the Iberian margin in the Atlantic Ocean. The Enderby Basin, a remote region between Kerguelen and the East Antarctic continental margin, displays similar features of this process. Unfortunately, poor geophysical data exist to describe the crustal structure, due to bad accessibility and rough weather conditions. As a consequence high risks are present to conduct such experiments. Since systematic and detailed magnetic data are not available for this area, the timing and orientation of the breakup between India, Australia and East Antarctic contain large un- certainties. Additionally, existing data display poor quality and resolution. Previous models support the theory that the northward drift of India was accelerated at some point. Magnetic anomaly interpretations led to different kinematic models that predict the initiation of the breakup around 118 Ma ago, 135 Ma or at an even older dispersal time. To support tectonic models and solve the enigma regarding the Gondwana breakup, new datasets of magnetic, gravimetric, seismic reflection and refraction data were acquired during two research cruises in 2007 and 2012. This thesis presents a new tectonic model for the geodynamic evolution of the Enderby Basin after the initial Gondwana breakup based on new seismic, magnetic and gravimetric data. We present a P-wave velocity profile which is based on the first seismic refraction profile acquired in the the area between Kerguelen and East Antarctica. The integrated interpretation of the data agrees with previous models about the dating of the Mac Robertson Anomaly. The breakup in this region can be dated at M9/ ∼ 128 Ma based on the magnetic anomaly data and the velocity model. We confirm theories of an breakup closer to the Cretaceous Normal Superchrone in the Enderby Basin which were under dispute for a long time. The model rejects the existence of an fossil spreading ridge, hence the breakup between India and Antarctica was continuous

A tree of Indo-African mantle plumes imaged by seismic tomography

International audienceMantle plumes were conceived as thin, vertical conduits in which buoyant, hot rock from the lowermost mantle rises to Earth’s surface, manifesting as hotspot-type volcanism far from plate boundaries. Spatially correlated with hotspots are two vast provinces of slow seismic wave propagation in the lowermost mantle, probably representing the heat reservoirs that feed plumes. Imaging plume conduits has proved difficult because most are located beneath the non-instrumented oceans, and they may be thin. Here we combine new seismological datasets to resolve mantle upwelling across all depths and length scales, centred on Africa and the Indian and Southern oceans. Using seismic waves that sample the deepest mantle extensively, we show that mantle upwellings are arranged in a tree-like structure. From a central, compact trunk below ~1,500 km depth, three branches tilt outwards and up towards various Indo-Austral hotspots. We propose that each tilting branch represents an alignment of vertically rising blobs or proto-plumes, which detached in a linear staggered sequence from their underlying low-velocity corridor at the core–mantle boundary. Once a blob reaches the viscosity discontinuity between lower and upper mantle, it spawns a ‘classical’ plume-head/plume-tail sequence

SubMachine: Web-Based Tools for Exploring Seismic Tomography and Other Models of Earth's Deep Interior

We present SubMachine, a collection of web‐based tools for the interactive visualization, analysis, and quantitative comparison of global‐scale data sets of the Earth's interior. SubMachine focuses on making regional and global‐scale seismic tomography models easily accessible to the wider solid Earth community, in order to facilitate collaborative exploration. We have written software tools to visualize and explore over 30 tomography models—individually, side‐by‐side, or through statistical and averaging tools. SubMachine also serves various nontomographic data sets that are pertinent to the interpretation of mantle structure and complement the tomographies. These include plate reconstruction models, normal mode observations, global crustal structure, shear wave splitting, as well as geoid, marine gravity, vertical gravity gradients, and global topography in adjustable degrees of spherical harmonic resolution. By providing repository infrastructure, SubMachine encourages and supports community contributions via submission of data sets or feedback on the implemented toolkits

Preliminary performance report of the RHUM-­RUM ocean bottom seismometer network around La Réunion, western Indian Ocean

RHUM-­RUM is a German-­French seismological experiment based on the sea floor surrounding the island of La Réunion, western Indian Ocean. Its primary objective is to clarify the presence or absence of a mantle plume beneath the Reunion hotspot. RHUM-­RUM's central component is a 13-­month deployment (Oct 2012 to Nov 2013) of 57 broadband ocean bottom seismometers (OBS) and hydrophones over an area of 2000x2000 km2 surrounding the hotspot. The array contained 48 broadband OBS from the German DEPAS pool and 9 stations from the French INSU pool. It has been the largest deployment of DEPAS and INSU OBS so far, and the first large joint experiment. We give an overview of station performance and issues encountered, touching on instrument responses, recorder and battery performance, noise characteristics, and data yield. Of the 57 stations, 46 had proper seismometer and 53 proper hydrophone recordings. Out of a installation time of 13x57=741 station-­months, 412 months of data were actually realized for the seismometers, and 710 for the hydrophones. At long periods (>10 s), the DEPAS stations are affected by significantly more noise than the INSU stations, a difference that is most pronounced on the horizontal components and can probably be explained by tilting of the instrument assemblage. The DEPAS sensors are integrated into the OBS frame and buoy assemblage, and would therefore record its motions, caused for example by the action of deep sea currents. However, this integrated setup also makes the DEPAS OBS easier to deploy and recover, especially in large deployments such as this one

Noise on broadband Ocean Bottom Seismometers (OBS) from the German (DEPAS) and French (INSU) instruments pools as recorded in the RHUM-RUM project

A long-standing discussion in the OBS community is about the influence of OBS design on noise levels of seismic records. We present results from the RHUM-RUM experiment in the Indian Ocean. RHUM-RUM is a German-French seismological experiment based on the sea floor surrounding the island of La Réunion, western Indian Ocean. RHUM-RUM’s central component is a 13-month deployment (Oct 2012 to Nov 2013) of 57 broad- and wideband ocean bottom seismometers (OBS) and hydrophones over an area of 2000x2000 km2 surrounding the hotspot. The array contained 48 wideband OBS from the German DEPAS pool and 9 broad-band OBS from the French INSU pool. It is the largest deployment of DEPAS and INSU OBS so far, and the first joint experiment. Therefore it allows to compare the performance of these distinct instrument types in different ocean-floor environments. The INSU seismic sensors stand away from their OBS frames, whereas the DEPAS sensors are integrated into theirs. At long periods (>10 s), the DEPAS seismometers are affected by significantly stronger noise than the INSU seismometers. On the horizontal components, this can be explained by tilting of the frame and buoy assemblage, e.g., through the action of ocean-bottom currents. However, the long period noise level on the vertical components suggests that the DEPAS intruments are also affected by significant self-noise of the CMG-40TOBS seismometer itself. By comparison, the INSU instruments (Trillium 240OBS sensors) are much quieter at periods >30 s and hence better suited for long-period studies. The trade-off of the instrument design is that the integrated DEPAS setup is easier to deploy and recover, especially when large numbers of stations are involved or fast deployment/recovery of the instruments is desired (e.g. active experiments). Additionally, the wideband sensor has only half the power consumption of the broadband INSU seismometers. This presentation also reviews network performance and data quality: Of the 57 stations, 46 and 53 yielded good seismometer and hydrophone recordings, respectively. The 19,751 total deployment days yielded 18,735 days of hydrophone recordings and 15,941 days of seismometer recordings, which are 94% and 80% of the theoretically possible yields

Preparing for InSight: Evaluation of the Blind Test for Martian Seismicity

ISSN:0895-0695ISSN:1938-205