Description: The lower third of the mantle is sampled extensively by body waves that diffract around the earth's core (Pdiff and Sdiff phases), which could deliver highly resolved tomographic images of this poorly understood region. But core-diffracted waves—especially Pdiff waves—are not often used in tomography because they are difficult to model adequately. Our aim is to make core-diffracted body waves usable for global waveform tomography, across their entire frequency range. Here we present the data processing part of this effort. A method is demonstrated that routinely calculates finite-frequency traveltimes of Pdiff waves by cross-correlating large quantities of waveform data with synthetic seismograms, in frequency passbands ranging from 30.0 to 2.7 s dominant period. Green's functions for 1857 earthquakes, typically comprising thousands of seismograms, are calculated by theoretically exact wave propagation through a spherically symmetric earth model, up to 1 Hz dominant period. Out of 418 226 candidates, 165 651 (39.6 per cent) source–receiver pairs yielded at least one successful passband measurement of a Pdiff traveltime anomaly, for a total of 479 559 traveltimes in the eight passbands considered. Measurements of teleseismic P waves yielded 448 178 usable source–receiver paths from 613 057 candidates (73.1 per cent success rate), for a total of 2 306 755 usable teleseismic dT in eight passbands. Observed and predicted characteristics of Pdiff traveltimes are discussed and compared to teleseismic P for this very large data set. Pdiff measurements are noise-limited due to severe wave attenuation with epicentral distance and frequency. Measurement success drops from 40–60 per cent at 80° distance, to 5–10 per cent at 140°. Frequency has a 2–3 times stronger influence on measurement success for Pdiff than for P . The fewest usable dT measurements are obtained in the microseismic noise band, whereas the fewest usable teleseismic P measurements occur at the highest frequencies. dT anomalies are larger for Pdiff than for P , and frequency dependence of dT due to 3-D heterogeneity (rather than just diffraction) is larger for Pdiff as well. Projecting the Pdiff traveltime anomalies on their core-grazing segments, we retrieve well-known, large-scale structural heterogeneities of the lowermost mantle, such as the two Large Low Shear Velocity Provinces, an Ultra-Low Velocity Zone west of Hawaii, and subducted slab accumulations under East Asia and Central America.

Description: We present two independent, automated methods for estimating the absolute horizontal misorientation of seismic sensors. We apply both methods to 44 free-fall ocean-bottom seismometers (OBSs) of the RHUM-RUM experiment ( http://www.rhum-rum.net/ ). The techniques measure the 3-D directions of particle motion of (1) P -waves and (2) Rayleigh waves of earthquake recordings. For P -waves, we used a principal component analysis to determine the directions of particle motions (polarizations) in multiple frequency passbands. We correct for polarization deviations due to seismic anisotropy and dipping discontinuities using a simple fit equation, which yields significantly more accurate OBS orientations. For Rayleigh waves, we evaluated the degree of elliptical polarization in the vertical plane in the time and frequency domain. The results obtained for the RHUM-RUM OBS stations differed, on average, by 3.1° and 3.7° between the methods, using circular mean and median statistics, which is within the methods’ estimate uncertainties. Using P -waves, we obtained orientation estimates for 31 ocean-bottom seismometers with an average uncertainty (95 per cent confidence interval) of 11° per station. For 7 of these OBS, data coverage was sufficient to correct polarization measurements for underlying seismic anisotropy and dipping discontinuities, improving their average orientation uncertainty from 11° to 6° per station. Using Rayleigh waves, we obtained misorientation estimates for 40 OBS, with an average uncertainty of 16° per station. The good agreement of results obtained using the two methods indicates that they should also be useful for detecting misorientations of terrestrial seismic stations.

Description: Petroleum systems located at passive continental margins received increasing attention in the last decade mainly because of deep- and ultra‐deep-water hydrocarbon exploration and production. The high risks associated with these settings originate mainly from the poor understanding of inherent geodynamic processes. The new priority program SAMPLE (South Atlantic Margin Processes and Links with onshore Evolution), established by the German Science Foundation in 2009 for a total duration of 6 years, addresses a number of open questions related to continental breakup and post‐breakup evolution of passive continental margins. 27 sub‐projects take advantage of the exceptional conditions of the South Atlantic as a prime “Geo‐archive.” The regional focus is set on the conjugate margins located east of Brazil and Argentina on one side and west of Angola, Namibia and South Africa on the other (Figure 1) as well as on the Walvis Ridge and the present‐day hotspot of Tristan da Cunha. The economic relevance of the program is demonstrated by support from several petroleum companies, but the main goal is research on fundamental processes behind the evolution of passive continental margins.

Description: The Yellowstone region of western North America presents an example of extreme mantle heterogeneity. According to our P-wave tomography, it accommodates the most massive pile of subducted ocean floor that accumulated anywhere under North America over the past 60+ million years, down to at least 1600~km depth. Paradoxically, Yellowstone is commonly considered a type locality for the exact opposite, a classical deep mantle plume. A robust low-velocity is indeed imaged in the mid mantle, but reaches no deeper than 1000~km, is surrounded by slab, and underlain by more slab. We present our updated finite-frequency model of North America, which now includes data from all of 2008 and 2009, specifically the recent USArray stations east of Yellowstone. We discuss some consequences of the imaged geometry. If a deep mantle plume is indeed present, its “ordinary” operation would seem to have been choked off for a long time interval (on the order of 60 Myr) by slab that was sinking onto it from above and is now located deeper than the current, slow mid-mantle anomaly. The Columbia River flood basalts around 17~Myr would then represent the revival of deep plume operation, rather than the original plume head. Alternatively, we might reject the classical plume hypothesis for Yellowstone, but this leaves us looking for the powerful heat source of the young flood basalts. The imaged geometry suggests a direct relationship to subduction, e.g. dewatering and melting around the 660-km discontinuity.

Description: The time has come to exploit the full richness of broadband, three-component waveforms. The inversion of full seismograms leads to a tremendous improvement in imaging resolution due to the ability to map structures that are smaller than the seismic wavelength. In addition, it provides important constraints on density and attenuation. State-of-the-art software for full waveform tomography is available in scientific environments but is not yet accessible to the practitioner. The Toolbox for Applied Seismic Tomography (TOAST) will open a new window to seismic inversion. Due to advances in available computational resources and recent developments in high performance and parallelized computing, 3D inversion of full seismograms is within reach. By combining tested code collections for waveform modelling and the solution of large inverse problems, complemented by experience in the management of large software projects and by sound expertise in the inversion of elastic waves from the centimeter to the kilometer scale, the cooperation of the TOAST project partners will provide a unique knowledge base for implementing flexible and efficient tools for full waveform tomography and to transfer the knowledge to industrial practice. The TOAST project pursues the concept of modularization. It will provide modules that interact through standardized interfaces and thereby can be re-combined in application-specific and efficient ways. The Toolbox for Applied Seismic Tomography will prove its worth through application to surveys from commercial practice. Existing data from seismic experiments at different scales (e.g., monitoring of embankments, CO2 sequestration studies) and newly aquired shallow seismic and ultrasonic data will serve as case studies to validate the functionality of the toolbox.

Description: We present a new technique to assess the moment tensor, source time function (STF) and depth of an earthquake, along with a full estimate of the uncertainties in each of these parameters. This methodology is being applied at the ISC (International Seismological Centre) to construct a new catalogue of earthquake point source models, referred to as ISC-PPSM (International Seismological Centre – Probabilistic Point Source Models). We employ a Bayesian inversion strategy to produce an ensemble of earthquake point source models that satisfactorily describe the P- and SH-waves observed tele-seismically at global broadband seismic stations. The methodology builds on the techniques proposed by Stähler & Sigloch (2014, 2016). Here we explore several ways of parameterising the earthquake STF, including describing the STF as a set of weighted harmonic functions, and describing the STF as the sum of multiple Gaussian spikes. ISC-PPSM is applied to moderate magnitude (5.5 – 7.2 Mw) earthquakes across the globe. As we jointly solve for the earthquake depth and STF, we can add new depth resolution to shallow (〈 40 km depth) moderate magnitude earthquakes, where the depth phases become subsumed within the STF. Additionally, the Bayesian inversion strategy allows us to assess the range of earthquake moment tensors that can describe the observed waveforms for a given event. This allows is to go some way towards constraining the variability in moment tensors reported to the ISC for many events.

Description: ORFEUS (Observatories and Research Facilities for European Seismology, orfeus-eu.org) coordinates and promotes seismology in the Euro-Mediterranean region through harmonized collection, archival and distribution of seismic waveform data & metadata, based on services and products managed at national level by more than 60 participating seismological Institutions. ORFEUS is one of the founding members of EPOS Seismology (www.epos-eu.org/tcs/seismology) and its services are largely integrated in the EPOS Data Access Portal (www.ics-c.epos-eu.org). ORFEUS comprises: (i) the European Integrated waveform Data Archive (EIDA; orfeus-eu.org/data/eida); (ii) the European Strong-Motion databases (orfeus-eu.org/data/strong); and iii) the recently established group representing the community of European mobile pools, including amphibian instrumentation (orfeus-eu.org/data/mobile). Currently, ORFEUS facilitates access to the waveforms acquired by more than 18,000 stations including dense temporary experiments (e.g., AlpArray, AdriaArray), with strong emphasis on open, high-quality data. Access to data and products is ensured through state-of-the-art technologies - with strong emphasis on web services - clear policies and licenses, and acknowledging the crucial role played by data providers. Significant efforts are underway to enhance the existing services to tackle the challenges posed by the Big Data Era and the needs of computational seismology, and to actively encourage interoperability and integration of multidisciplinary datasets in geoscience workflows. ORFEUS also implements community services that include software and travel grants, webinars, workshops, editorial initiatives and discussion forums. ORFEUS activities are assessed and improved through the interaction with a User Advisory Group, which comprises European Earth scientists with expertise on a broad range of disciplines.