ALBERT

Description: Traditionally, the P-to-S receiver function is widely used to map velocity boundaries at continents. In this study, we present a novel observation of P660sP and PS660P phases which involve P-to-S conversion at the 660-km discontinuity and arrive as postcursors of surface-reflected PP waves in the context of receiver function technique. We collect US transportable Array seismic data for M≥6.0 earthquakes in the distance range of 70°~120° and calculate receiver functions up to 350 seconds after P arrival. Receiver function stacks with PP bounce points at the central Pacific show robust detection of PP postcursors. After the removal of interfering phases using an f-k filter, the amplitude of PP postcursors from the 660 systematically increases with the epicentral distance in the range of 80°~110°, inconsistent with a laterally homogeneous and isotropic medium. A localized anisotropy layer near the 660-km discontinuity beneath the central Pacific is required by the data. The anisotropy layer may represent the segregation of ultra-deep carbonatite melts under strong shear deformation induced by mantle upwellings. Our findings support the notion of efficient magmatic release of carbo to the exosphere away from cold downwellings and provide insights into the global carbon cycle.  The novel application of receiver function technique provides a new opportunity to constrain transition zone seismic discontinuities beneath oceanic plates with high resolution, complementing existing techniques and ongoing OBS deployments.

Description: Transition zone seismic discontinuities (TZSDs) at depths of about 410 and 660 km are generally attributed to phase transitions in the olivine system. They offer great insights into the temperature, composition, and dynamics of Earth’s interior. A detailed characterization of the seismic structure near the discontinuity, such as shear velocity and density jump, and the transition width, is essential for inferring the thermos-chemical properties near the transition zone and understanding the tectonic processes. While numerous studies have investigated TZSDs with diverse datasets, few have simultaneously obtained robust observations of these properties. Converted waves (Pds) from the discontinuities are sensitive to shear velocity structure near the discontinuity and top-side reflections (PpPds) are more sensitive to the density. A joint analysis of the two waves allows us to independently constrain the seismic features near the TZSDs. We propose a simultaneous inversion of the shear velocity and density jump, as well as transition width and velocity gradient near the TZSDs using multiband (15 sec ~ 1 Hz) amplitudes and traveltimes of Pds and PpPds waves. We apply joint analysis of converted waves and topside reflected waves in the context of teleseismic P-wave receiver function technique at several large seismic arrays (USArray, China Array, Australian National Network, African Array, etc.) and compare the discontinuity structures across continents. These new descriptions will serve as the basis for exploring compositional models of the transition zone and understanding its relationship with prior and ongoing tectonic processes.

Description: The majority of geochemical and cosmochemical research is based upon observations and, in particular, upon the acquisition, processing and interpretation of analytical data from physical samples. The exponential increase in volumes and rates of data acquisition over the last century, combined with advances in instruments, analytical methods and an increasing variety of data types analysed, has necessitated the development of new ways of data curation, access and sharing. Together with novel data processing methods, these changes have enabled new scientific insights and are driving innovation in Earth and Planetary Science research. Yet, as approaches to data-intensive research develop and evolve, new challenges emerge. As large and often global data compilations increasingly form the basis for new research studies, institutional and methodological differences in data reporting are proving to be significant hurdles in synthesising data from multiple sources. Consistent data formats and data acquisition descriptions are becoming crucial to enable quality assessment, reusability and integration of results fostering confidence in available data for reuse. Here, we explore the key challenges faced by the geo- and cosmochemistry community and, by drawing comparisons from other communities, recommend possible approaches to overcome them. The first challenge is bringing together the numerous sub-disciplines within our community under a common international initiative. One key factor for this convergence is gaining endorsement from the international geochemical, cosmochemical and analytical societies and associations, journals and institutions. Increased education and outreach, spearheaded by ambassadors recruited from leading scientists across disciplines, will further contribute to raising awareness, and to uniting and mobilising the community. Appropriate incentives, recognition and credit for good data management as well as an improved, user-oriented technical infrastructure will be essential for achieving a cultural change towards an environment in which the effective use and real-time interchange of large datasets is common-place. Finally, the development of best practices for standardised data reporting and exchange, driven by expert committees, will be a crucial step towards making geo- and cosmochemical data more Findable, Accessible, Interoperable and Reusable by both humans and machines (FAIR).