ALBERT

Description: A pronounced warm anomaly occurred at the Peruvian coast in early 2017. This “Coastal Niño” caused heavy rainfalls, leading to flooding in Peru and Ecuador. At the same time, neutral conditions prevailed in the equatorial Pacific. Using observational sea surface temperature data sets and an ocean reanalysis product for the time period 1900 to 2010, previous similar events are investigated. Eighteen coastal warming events without corresponding equatorial Pacific warming are identified. Further analysis shows, however, that only four of these events are not connected to the central equatorial Pacific. All other periods of strong coastal warm anomalies are directly followed or preceded by El Niño-like conditions. The “stand-alone” coastal warming events are characterized by comparatively low equatorial heat content. We thus hypothesize that the depleted heat content in the equatorial Pacific in the wake of the strong 2015/2016 El Niño prevented the warming to spread westward in 2017.

Description: Data from the Projecto de Investigacion Sismologica de la Cordillera Occidental (PISCO) seismic network and from six broadband seismographs that were operating in northern Chile were used to investigate the mantle in the convergent boundary zone between Nazca plate and the South American continent for the presence of anisotropy. Broadband data as well as long-period filtered data of teleseismic SKS and PKS phases were analyzed for the presence of shear wave splitting as a possible indicator for seismic anisotropy in the mantle beneath the PISCO network. Measurable shear wave splitting was observed with maximum delay times between the slow and fast split wave of the order of 1 s. Splitting of S waves from intermediate-depth events located directly beneath the PISCO network in the descending Nazca plate is generally associated with small delay times of the order of 0.1 s, a value typical for the continental crust. Near-vertical ScS reflections from two deep earthquakes in Argentina and one nearby intermediate-depth earthquake have similar splitting parameters as the SKS phases. This means that the anisotropic zone causing the splitting of the core phases can be constrained to the Pacific mantle underlying the subducting Nazca plate. It probably does not extend deeper than about 260 km. The majority of the anisotropy directions inferred from the core phases are parallel to the absolute plate motion (APM) direction of the Nazca plate, which is about N80°E. At some stations, however, the fast polarization direction is pointing N160°E, nearly parallel to the strike of the trench and the Andes which would be compatible with the trench-parallel flow model for South America proposed by Russo and Silver [1994]. This direction is observed over an approximately 100-km-wide band to the west of the active volcanic zone. It may represent either a second anisotropy regime in the mantle, a small-scale diversion of slab-entrained mantle flow, or a relatively small area where slab entrainment of mantle flow is reduced or ceases to exist. The large number of observed APM-parallel fast directions suggests, however, that the mantle beneath the descending Nazca plate in northern Chile deforms mainly as the result of slab-entrained mantle flow. The large variations of anisotropy directions in the Andean subduction zone indicate that asthenospheric flow in the Pacific mantle has a complex pattern which may vary over scale lengths of a few hundred kilometers and which may be governed by slab morphology.

Description: The International Lithosphere Program (ILP) was established in 1980 as the Inter-Union Commission on the Lithosphere (ICL) by the International Council for Science (ICSU), following a request from the International Union of Geodesy and Geophysics (IUGG) and the International Union of Geological Sciences (IUGS). In 2005 ICSU transferred its sponsorship to IUGG and IUGS. The ILP focusses on the nature, dynamics, origin, and evolution of the lithosphere, with special attention to the continents and their margins. Targeting these goals through international and interdisciplinary collaboration, ILP established several task forces and coordinating committees to pursue specific research objectives. Topics always follow one of the four ILP themes: global change, contemporary dynamics and deep processes, continental lithosphere, and ocean lithosphere. ILP’s funding is limited to five year periods and just understood as seed money. In the last four decades ILP was involved in the composition and set up of a number of worldwide leading light house projects: The GSHAP (Global Seismic Hazard Map), the ICDP (International Continental Drilling Project), the WSM (World Stress Map Project), the TOPO-Europe project and its follow up initiatives TOPO-Asia, TOPO Iberia – just to name a few. Currently ILP supports new initiatives on digitalization. With its Flinn-Hart Award (until 2007 Hart Award), honouring outstanding young scientists for contributions in the field of solid Earth sciences, ILP motivated and promoted a generation of early career scientists. The new Evgueni Burov Medal from ILP, established in 2018, pays tribute to an outstanding researcher in solid Earth sciences and recognizes pioneering contributions by mid-career scientists.