Propagation of the Primorsky Fault in the central part of Lake Baikal and the evolution of Maloe More

The Primorsky Fault is one of the two major western boundary faults in the central part of Lake Baikal. According to the existing fault growth model (e.g. Agar and Klitgord, 1995), this fault has propagated gradually in a southward direction. During this propagation, the Primorsky Fault has cut through the footwall of the Ol’khon Fault, which is the other major boundary fault 35–40km to the south-east. This propagation has controlled the submergence of the Ol’khon Region which forms a large tilted block between both faults.Based on the interpretation of high-resolution reflection seismic profiles of the submerged part of the Ol’khon Region (ie. Maloe More), different depocentres have been identified in the hanging-wall region of the Primorsky Fault. These depocentres correspond to small basins that are separated from each other by distinct basement ridges, with an orientation that strikes almost perpendicularly to the Primorsky Fault. The occurrence of the oldest sedimentary deposits (Unit A, Miocene age) in depocentres in the southern part of Maloe More, indicates that old sedimentary traps and lacustrine environments must have existed in the area. This finding contradicts the existing growth model for the Primorsky Fault, which assumes that only a recent (ca. 1Ma) and gradual propagation of the fault is responsible for the increasing subsidence in Maloe More. In the different sub-basins, younger sediments (Unit B, Upper Pliocene) overlie the deposits of Unit A. Nevertheless, the upper parts of Unit B are also present on the different basement ridges. The thickness of Unit B is on the northeastern ridges in Maloe More considerably greater than on those more to the south-west, indicating that they have been submerged for a longer time. Careful investigation of a RESURS satellite image of the area has revealed a possible segmentation of the Primorsky Fault, with segment boundaries occurring at the location of the different basement ridges in Maloe More.We believe that the growth of the Primorsky Fault can therefore be described in two different stages. A first stage, during the deposition of Unit A, was characterised by the evolution of 5 different (isolated) segments that defined small basins in Maloe More. The observed basement ridges corresponded at that time to intrabasin highs that resulted from the displacement deficit between the different fault segments. Increasing extension lead to the further growth of the segments, causing a final linkage between them. This linkage marks the onset of a second stage, which was achieved during the deposition of Unit B. Linkage between fault segments caused a displacement increase (mainly at the former location of the segment boundaries), resulting in the submergence of the basement ridge. Seen the thicker deposits of Unit B on the northeastern ridges in Maloe More, we believe that the segment linkage was first established between the northernmost fault segments of the Primorsky Fault. Subsequent linkages between other segments more to the south, and the associated post-linkage displacement increases, caused the further submergence of Maloe More towards the southwest in later stages

The Hazar pull-apart along the East Anatolian Fault: Structure and active deformation

Understanding the irregularity of seismic cycles: A case study in Turke

Holocene earthquake-triggered mass-wasting events recorded in the sediments of Lake Puyehue (South-Central Chile)

Despite South-Central Chile’s high seismicity and the occurrence of earth’s largest instrumentally recorded earthquake (AD 1960; Mw: 9.5), paleoseismic data is still scarce for this region. In this study, very high-resolution reflection seismic profiles (3.5 kHz) in Lake Puyehue (41°S) were utilized to trace giant seismic events back into time. The seismic profiles show repeated occurrences of multiple mass-wasting deposits (slumps, debris flows, homogenites) occurring at a same seismic-stratigraphic horizon, indicating that they are coeval and caused by a single mass-wasting event of basin-wide importance. An age-depth model, based on 9 AMS radiocarbon datings and varve-counting on an 11 m-long sediment core, has been used to develop a “seismic chronostratigraphy”. It allows dating of the mass-wasting events by interpolation between dated seismic horizons to the distal parts of the mass-wasting deposits. The mass-wasting events are assumed to be earthquake-triggered because:The recentmost mass-wasting events correlate with the devastating historical earthquakes of AD 1575 and AD 1960.Synchronicity of multiple slope failures (mass-wasting events) requires a strong regional trigger, such as an earthquake. Consequently, local slope oversteepening at delta fronts or local fluid expulsion could not initiate such widespread events.South-Central Chile has been historically subjected to several strong (M > 8) subduction earthquakes and subduction processes have been constantly active since Mesozoic times.Multiple slope failures occur at water depths > 70 m, which rules out shallow instability triggers, such as storm wave action and lake-level fluctuations.This study reveals nine paleoseismic events during the Holocene with a mean recurrence rate of about 1000 yr, but with an overall relatively aperiodic occurrence (ranging between 400-2000 yrs.). The most prominent event took place around 1660 cal. yr. BP, evidenced by at least 29 simultaneous mass-movements and a homogenite deposit. Quantitative comparison of mass-wasting events related to the historical earthquakes of AD 1960 and AD 1575 showed significant differences (respectively 17 and 4 observed mass-wasting deposits) although these earthquakes are assumed to have had a comparable strength. This can be attributed to a lowered sedimentation rate on the potentially unstable slopes in the period 3000 cal. yr. BP – 500 cal. yr. BP, which would have made lacustrine earthquake recording less likely in AD 1575. The absence of mass-wasting deposits associated with other historical earthquakes (e.g.: AD 1737 (Ms: 7.5) and AD 1837 (Ms: 8)) indicates that only mega-earthquakes (Mw >8.5) within a range of about 300 km are recorded in the sedimentary sequence of Lake Puyehue.Reflection seismic profiles also show vertical fluidisation structures with large-scale sediment injections, which disturb the upper sedimentary sequences. The top of these fluidisation structures and diverse deformation levels could be spatially linked to seismically induced mass-wasting deposits and consequently indicate an additional method for lacustrine paleo-earthquake tracing.Several reconaissance seismic surveys on other glacigenic lakes in the Chilean Lake District also show promising paleoseismic records, which will offer the opportunity to correlate lacustrine records to reveal South-Central Chile’s paleoseismic history in detail and the earthquake registration capacities of its glacigenic lakes

Submeter mapping of methane seeps by ROV observations and measurements at the Hikurangi Margin, New Zeeland

During R.V. Sonne cruise SO191-3, part of the "New (Zealand Cold) Vents" expedition, RCMG deployed their CHEROKEE ROV "Genesis" on the Hikurangi Margin. This accretionary margin, on the east coast of New Zealand, is related to the subduction of the Pacific Plate under the Australian Plate. Several cold seep locations as well as an extensive BSR, indicating the presence of gas hydrates, have been found at this margin. The aim of the ROV-work were to precisely localize active methane seeps, to conduct detailed visual observations of the seep structures and activity, and to perform measurements of physical properties and collect samples at and around the seep locations. The ROV allowed first ever visual observations of bubble-releasing seeps at the Hikurangi Margin. Seeps were observed at Faure Site and LM-3 in the Rock Garden area, at a flat to moderately undulating sea floor where soft sediments alternate with carbonate platforms. Bubble-releasing activity was very variable in time, with periods of almost non-activity (5 bubbles/second) alternating with periods of violent outbursts (190 bubbles/second). Bubbles sizes ranged from less than 5 mm to more than 20 mm. At Faure Site, bubble release was monitored over a period of 20 minutes, resulting in the observation of 6 outbursts, each lasting 1 minute at a 3 minute interval. These violent outbursts were accompanied by the displacement and resuspension of sediment grains and the formation of small depressions showing what is possibly an initial stage of pockmark formation. At the LM-3 site only some small bubble seeps were observed near a large carbonate platform covered by Bathymodiolus mussels, Calyptogena shells and tube worms. Sediment-temperature measurements, in both areas, were largely comparable with the bottom-water temperature except at LM-3, at a site densely populated by polychaetes, where anomalous low sediment-temperature was measured. Overall, both seep areas are very confined in space and bottom-water sampling revealed that the released methane has a microbial signature

Geophysical characterization of the sedimentary environments in Lago Puyehue and Lago Icalma (Chilean Lake District, SW Andes)

The Chilean Lake District, located in Southern Chile, comprises 17 lakes at the foothill of the Cordillera de los Andes. These lakes, dammed by frontal moraines, were formed during the last deglaciation (12500-12000 BP). Their sedimentary infilling has the potential to contain a complete and continuous Holocene sedimentary record of environmental and climatic changes having affected the area.High-resolution reflection seismic data (sparker and pinger) collected during the 2001-2002 expedition in the framework of the Belgian ENSO-CHILE project have allowed us to select two lakes for the collection of long and short sediment cores:Lago Icalma (38°50’S, alt. 1150 m) is located in the Cordillera de los Andes, in the upper part of the Bio-Bio River. Its watershed (148 km2) is dominated by a soft post-glacial sediment cover, interrupted by two important pumice layers. According to the high-resolution seismic survey, the 70m-thick sedimentary infilling consists of morainic deposits, under- and interflows and laminated lacustrine deposits. The western part of the main basin represents an elevated platform, free of the influence of bottom-currents and turbidites and possibly consisting of interflow deposits. Core descriptions and physical property analyses of sediments (gamma-density, low and high-resolution magnetic susceptibility) suggest that the deposits consist of an alternation of volcanic deposits and terrigenous sediments correlated on pinger profiles, showing the presence of several low-amplitude layers.Lago Puyehue (40°40’S, alt. 185 m) is located at the foothill of the Cordillera de los Andes and presents a glacial morphology much more complicated than Lago Icalma. Its watershed is larger (1267 km2) and dominated by Quaternary and Tertiary volcanic rocks. The lake is composed, in its western part, by a large basin, filled by 250 m of sediments, as can be deduced from sparker profiles. The eastern part of the lake presents a complex substratum morphology. However, it was possible to find a suitable location in underflow and interflow deposit areas for the collection of two long cores. Core description and physical property analyses of sediments of the interflow area suggest a good and continuous sedimentary record.With this contribution, we wish to illustrate the potential of high resolution geophysical site-survey data for interpreting core descriptions and physical property analyses

Challenges in recruiting children to a multidrug-resistant TB prevention trial

BACKGROUND: Recruitment to randomised clinical trials can be challenging and slow recruitment has serious consequences. This study aimed to summarise and reflect on the challenges in enrolling young children to a multidrug-resistant TB (MDR-TB) prevention trial in South Africa. METHODS: Recruitment to the Tuberculosis Child Multidrug-resistant Preventive Therapy Trial (TB-CHAMP) was tracked using an electronic recruiting platform, which was used to generate a recruiting flow diagram. Structured personnel questionnaires, meeting minutes and workshop notes were thematically analysed to elucidate barriers and solutions. RESULT: Of 3,682 (85.3%) adult rifampicin (RIF) resistant index cases with pre-screening outcomes, 1597 (43.4%) reported having no children under 5 years in the household and 562 (15.3%) were RIF-monoresistant. More than nine index cases were pre-screened for each child enrolled. Numerous barriers to recruitment were identified. Thorough recruitment planning, customised tracking data systems, a dedicated recruiting team with strong leadership, adequate resources to recruit across large geographic areas, and excellent relationships with routine TB services emerged as key factors to ensure successful recruitment. CONCLUSION: Recruitment of children into MDR-TB prevention trials can be difficult. Several MDR-TB prevention trials are underway, and lessons learnt from TB-CHAMP will be relevant to these and other TB prevention studies

Normal versus earthquake-induced clastic sedimentation processes in Lago Puyehue, Chilean Lake District, 41°S

The recent evolution of clastic sedimentary processes in Lago Puyehue, as characterized by high-resolution seismic profiling and multidisciplinary analysis of sediment cores from two contrasted coring sites (PU-I and PU-II), is presented and compared to the catastrophic impact of the 1960 Chilean earthquake (Mw 9.5). Lake Puyehue’s catchment area was strongly influenced by this earthquake: (i) multiple earthquake-induced land slides and debris avalanches temporally dammed the course of the main tributary (Rio Golgol) and (ii) ca. 7.106 m3 of white fine pumiceous sands and black medium-sand-sized scoria were deposited in the catchment area during the Puyehue-Cordon-Caulle volcanic eruption that followed two days after the main seismic shock.Based on the correlation of seismic data and sediment cores dated by 137Cs and the identification of historical events, we argue that “normal” clastic sedimentation is essentially resulting from the development of homopycnal flows at the end of the winter season in these oligothrophic monomictic lakes from the Chilean Lake District. While distal clastic environments (PU-II coring site) are dominated by a biogenic production and appear to have been little affected by the 1960 earthquake and Puyehue volcanic eruptions in 1960 and 1921-22, this might not be the case for more proximal clastic environments (PU-I coring site) as well submitted to sporadic hyperpycnal flows during major flood events. In 1960, for example, as several landslide dams broke in the Golgol valley after the earthquake and the volcanic eruption, a mega-hyperpycnal flow reworked a mixture of volcanoclastic and soils sediments from the catchment as well as lacustrine sediments surrounding the Golgol delta during the rising limb of the flood and accumulated ca. 3.106 m3 of material in the deep basin

Exposure-age record of Holocene ice sheet and ice shelf change in the northeast Antarctic Peninsula

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