Algorithms for automatic,real-time tsunami detection in wind–wave measurements Part I: Implementation strategies and basic tests

Several, although not all, wind–wave gages are equipped with sensors capable of detecting sea-level oscillations within the tsunami frequency band. The present paper looks at the algorithms to be implemented in the software of these gages in order to automatically perform the real-time detection of a possible tsunami within recorded signals. In particular, a new algorithm is proposed and tested. The first part of the paper concentrates on the algorithms' characteristics, implementation strategies and basic testing. First of all, the situations in which wind–wave measurements are either essential, or useful for real-time tsunami detection are discussed. In the second place, already existing algorithms are recalled, specifying their characteristics and fields of application. Then, the characteristics of the new proposed algorithm – mainly based on an infinite impulse response, time domain filter – are illustrated and analyzed. Performance and efficiency of the considered algorithms are compared using synthetic time series. The second part of the paper discusses the algorithms' use in the framework of Tsunami Early Warning Systems (TEWS), testing them in actual cases.     

Mesoscale and microscale shock effects in the LL6 S4 chondrites Saint‐Séverin and Elbert: A tale of two breccias

Saint‐Séverin and Elbert, two LL6 chondrite breccias, were systematically studied to evaluate multiple deformation effects on spatial scales ranging from thin section (mesoscale) to micron‐submicron (microscale) using optical microscopy, electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). The different techniques provide consistent results but have complementary strengths, together providing a powerful approach to unravel even complex impact histories. Both meteorites have an S4 conventional shock stage, but interclast areas are more deformed, and clasts are more deformed in Elbert than in Saint‐Séverin. TEM and EBSD data provide compelling evidence that Saint‐Séverin experienced significant shock deformation while already hot, and cooled rapidly afterward, as a result of a major, possibly disruptive impact on the LL chondrite parent body ~4.4 Ga ago. In contrast, Elbert was shocked from a cold initial state but was heated significantly during shock, and cooled in a localized hot impact deposit on the LL asteroid. Both meteorites probably were shocked at least twice; data for Saint‐Séverin are best reconciled with a three‐impact model.     

Late Miocene evaporite geochemistry of Lorca and Fortuna basins (Eastern Betics,SE Spain): Evidence of restriction and continentalization

The Lorca and Fortuna basins are two intramontane Neogene basins located in the eastern Betic Cordillera (SE Spain). During the Late Tortonian—Early Messinian, marine and continental evaporites precipitated in these basins as a consequence of increased marine restriction and isolation. Here we show a stratigraphic correlation between the evaporite records of these basins based on geochemical indicators. We use SO₄ isotope compositions and Sr isotopic ratios in gypsum, and halite Br contents to characterize these units and to identify the marine or continental source of the waters feeding the evaporite basins. In addition, we review the available chronological information used to date these evaporites in Lorca (La Serrata Fm), including a thick saline deposit, that we correlate with the First Evaporitic Group in Fortuna (Los Baños Fm). This correlation is also supported by micropalaeontological data, giving a Late Tortonian age for this sequence. The Second Evaporitic Group, (Chicamo Fm), and the Third Evaporitic Group (Rambla Salada Fm) developed only in Fortuna during the Messinian. According to the palaeogeographical scheme presented here, the evaporites of the Lorca and Fortuna basins were formed during the Late Tortonian—Early Messinian, close to the Betic Seaway closure. Sulphate isotope compositions and Sr isotopic ratios of the Ribera Gypsum Mb, at the base of the Rambla Salada Fm (Fortuna basin), match those of the Late Messinian selenite gypsum beds in San Miguel de Salinas, in the near Bajo Segura basin (40 km to the East), and other Messinian Salinity Crisis gypsum deposits in the Mediterranean. According to these geochemical indicators and the uncertainty of the chronology of this unit, the assignment of the Rambla Salada Fm to the MSC cannot be ruled out.     

High-Frequency Response of the Atmospheric Electric Potential Gradient Under Strong and Dry Boundary-Layer Convection

The spectral response of atmospheric electric potential gradient gives important information about phenomena affecting this gradient at characteristic time scales ranging from years (e.g., solar modulation) to fractions of a second (e.g., turbulence). While long-term time scales have been exhaustively explored, short-term scales have received less attention. At such frequencies, space-charge transport inside the planetary boundary layer becomes a sizeable contribution to the potential gradient variability. For the first time, co-located (Évora, Portugal) measurements of boundary-layer backscatter profiles and the 100-Hz potential gradient are reported. Five campaign days are analyzed, providing evidence for a relation between high-frequency response of the potential gradient and strong dry convection.     

The structure of the lower crust at the Argentine continental margin, South Atlantic at 44°S

It is well established that the Argentine passive margin is of the rifted volcanic margin type. This classification is based primarily on the presence of a buried volcanic wedge beneath the continental slope, manifested by seismic data as a seaward dipping reflector sequence (SDRS). Here, we investigate the deep structure of the Argentine volcanic margin at 44°S over 200 km from the shelf to the deep oceanic Argentine Basin. We use wide-angle reflection/refraction seismic data to perform a joint travel time inversion for refracted and reflected travel times. The resulting P-wave velocity-depth model confirms the typical volcanic margin structure. An underplated body is resolved as distinctive high seismic velocity (v_p up to 7.5 km/s) feature in the lower crust in the prolongation of a seaward dipping reflector sequence. A remarkable result is that a second, isolated body of high seismic velocity (v_p up to 7.3 km/s) exists landward of the first high-velocity feature. The centres of both bodies are 60 km apart. The high-velocity lower-crustal bodies likely were emplaced during transient magmatic–volcanic events accompanying the late rifting and initial drifting stages. The lateral variability of the lower crust may be an expression of a multiple rifting process in the sense that the South Atlantic rift evolved by instantaneous breakup of longer continental margin segments. These segments are confined by transfer zones that acted as rift propagation barriers. A lower-crustal reflector was detected at 3 to 5 km above the modern Moho and probably represents the lower boundary of stretched continental crust. With this finding we suggest that the continent–ocean boundary is situated 70 km more seaward than in previous interpretations.     

Fine-Scale Measurements Of Turbulence In The Lower Troposphere: An Intercomparison Between A Kite- And Balloon-Borne, And A Helicopter-Borne Measurement System

Two state-of-the-art, high-resolution, in situ turbulence measurement systems, which can be deployed at altitudes well above the atmospheric surface layer, are compared: the Tethered Lifting System (TLS) of the Cooperative Institute for Research in Environmental Sciences (CIRES)at the University of Colorado, Boulder, Colorado, and the helicopter-borneturbulence measurement system HELIPOD of the Technical UniversityBraunschweig, Germany, and the University of Hanover, Germany. Whilethe CIRES TLS is a fixed-point platform, HELIPOD is a moving platform.On the basis of data taken with the two systems in separate field campaigns,the system capabilities are quantified and discussed. Criteria for instrumentalrequirements are presented. It is shown that both the CIRES TLS and HELIPODare well suited for measuring fine-scale turbulence that is characterized by very small temperature structure parameters 10⁶ K² m^–2/3 and smaller) and very small energy dissipation rates (10^-7 m² s^-3 and smaller). The authors are not aware of any other turbulence measurement systems that have similar capabilities and can be deployed at altitudes of up to several kilometres. The HELIPOD is ideal for high-resolution horizontal measurements while the TLS is ideal for high-resolution vertical measurements using multiple sensors attached to a suspended line.     

Geometry of growth strata in a transpressive fold belt in field and analogue model: Gosau Group at Muttekopf,Northern Calcareous Alps,Austria

The thrust sheets of the Northern Calcareous Alps were emplaced during Late Cretaceous thrust‐dominated transpression expressed by thrust sheets segmented by closely spaced tear faults. Thrust sheet‐top sediments were deposited during thrusting and associated fold growth and were controlled by active folding and tearing. We observe two types of angular unconformities: (1) Angular unconformities above folds between tear faults conform with the model of progressive unconformities. Across these unconformities dip decreases upsection. (2) Here, we define progressive unconformities that are related to tear faults and are controlled by both folding and tearing. Across these unconformities both strike and dip change. In growth strata overlying folds dissected by high‐angle faults, such unconformities are expected to be common. We used analogue modelling to define the geometry of the tear faults and related unconformities. Within the syn‐tectonic sediments, a steep, upward flattening thrust within a broader, roughly tulip‐shaped drag zone develops. The thrust roots in the tear fault in pre‐tectonic deposits and is curved upward toward the downthrown block. Vertical offset on the thrust is related to differential vertical uplift caused by, for example, growth of folds with different wavelength and amplitude on either side of the tear fault. Formation of progressive unconformities is governed by the relationship between the rates of deposition and vertical growth of a structure. Fault‐related progressive unconformities are additionally controlled by the growth of the vertical step across the tear fault. When the rates of vertical growth of two neighbouring folds separated by a tear fault are similar, the rate of growth across the tear fault is small; if the first differ, the latter is high. Episodic tear fault activity may create several angular unconformities attached to a tear fault or allow the generation of angular unconformities near tear faults in sedimentary systems that have a rate of deposition too high to generate classical progressive unconformities between the tear faults.     

Changes in the northern Gulf of St. Lawrence ecosystem estimated by inverse modelling: Evidence of a fishery-induced regime shift?

Mass-balance models have been constructed using inverse methodology for the northern Gulf of St. Lawrence for the mid-1980s, the mid-1990s, and the early 2000s to describe ecosystem structure, trophic group interactions, and the effects of fishing and predation on the ecosystem for each time period. Our analyses indicate that the ecosystem structure shifted dramatically from one previously dominated by demersal (cod, redfish) and small-bodied forage (e.g., capelin, mackerel, herring, shrimp) species to one now dominated by small-bodied forage species. Overfishing removed a functional group in the late 1980s, large piscivorous fish (primarily cod and redfish), which has not recovered 14 years after the cessation of heavy fishing. This has left only marine mammals as top predators during the mid-1990s, and marine mammals and small Greenland halibut during the early 2000s. Predation by marine mammals on fish increased from the mid-1980s to the early 2000s while predation by large fish on fish decreased. Capelin and shrimp, the main prey in each period, showed an increase in biomass over the three periods. A switch in the main predators of capelin from cod to marine mammals occurred, while Greenland halibut progressively replaced cod as shrimp predators. Overfishing influenced community structure directly through preferential removal of larger-bodied fishes and indirectly through predation release because larger-bodied fishes exerted top-down control upon other community species or competed with other species for the same prey. Our modelling estimates showed that a change in predation structure or flows at the top of the trophic system led to changes in predation at all lower trophic levels in the northern Gulf of St. Lawrence. These changes represent a case of fishery-induced regime shift.     

Intense extreme hydro-climatic events take a toll on society

Natural Hazards - In March 2019, the Iranian meteorological organization warned of the formation of several dense precipitation systems throughout the country. This was followed by a chain of storm...