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This work exposes some features of the landscape that enable us to determine neotectonic activity in the internal sector of the cordillera (35°30'S - 70°15'W). Through field observations, there were recognized lacustrine deposits characterized by laminated sands, silts, and clays, which records the sedimentation in a paleolake during a stage of the Last Glacial Maximum. The age of the deposits is inferred from their position in relation to a frontal moraine attributed to the last glaciation. Based on a sedimentary profile in the lacustrine deposits, there are described soft-sediment deformation structures and tectonic faults, one of them named El Seguro fault, presents 4 m of displacement measured along the fault plane, and an inverse movement. Morphological features indicate a seismic trigger, proposing the activity of the fault as a possible source. The frequency and distribution of >0.1 km2 mass movement deposits and their location close to the active structures allow us to identify an accumulation of landslides around them. Although many factors have favored these movements as lithology, steep slopes and pos-glacial relief, their position in the landscape suggest that seismic activity accelerated the development of large mass movements. Finally, it is proposed that tectonic activity has taken place during the Pleistocene-Holocene inclusive, with earthquakes of magnitude Ms =6, so that El Seguro fault could be an active fault at present. [ABSTRACT FROM AUTHOR]

A review of the literature suggests that the seismic process in Fennoscandia (the Baltic Shield) is affected by at least four mechanisms: (1) northwest-to-southeast movement of the lithospheric plate under the Norwegian and Barents seas by spreading of the Mid-Atlantic Ridge from Iceland to Spitsbergen; (2) postglacial isostatic uplift; (3) local recent neotectonic movements; and (4) gravitational bending deformations on continental contact with the sea shelf along the Norwegian coast due to strong erosion from the rising crystalline domain of the Baltic Shield. The current seismicity of Fennoscandia is relatively low. The strongest earthquake in this area over the last 1000 years was the earthquake of 1627 which had a magnitude of M ≈ 6.5 and occurred in the Kandalaksha graben in the White Sea. However, Fennoscandia, including the Kola Peninsula and eastern Karelia, has a reliable history of a significant number of Pleistocene and even Holocene paleoseismic dislocations, whose parameters allow them to be associated with strong earthquakes which occurred at that time with magnitudes of 7–8 and even higher. It is likely that these paleo-events occurred at the last stage of the glacial age (9000–10 000 years ago) during the intense postglacial isostatic uplift of the Fennoscandia domain. Their possible recurrence can be estimated as tens of thousands of years from the time interval between consecutive glaciations. One should therefore recognize that the nature of current seismicity of Fennoscandia is determined by tectonic stresses caused by both the global effect of the northwestern uplifting lithospheric plate under the Norwegian Sea (a constant source of tectonic stress accumulation) and local tectonic uplifts (the north coast of Norway) or lowerings (the Swedish coast of the Gulf of Bothnia), rather than by postglacial stresses. In addition, the increased seismicity of southwestern Norway and the adjacent North Sea shelf is most likely caused by the formation of crest-like structures under the action of tensile stresses revealed here. [ABSTRACT FROM AUTHOR]

Maio, C.V.; Crowell, A.L.; Sullivan, R.M.; Buzard, R.M.; Whitley, M.A.; Bogardus, R.C., and de Wit, C.W., 2019. Examining coastal dynamics and archaeological site evidence at a drowned cirque basin influenced by earthquakes and Little Ice Age glaciation. Journal of Coastal Research, 35(4), 814–834. Coconut Creek (Florida), ISSN 0749-0208. This study contributes baseline information regarding the framework geology, drivers of coastal change, and archaeological record along the fjord-indented coastlines of southcentral Alaska. Field data were collected in July 2015 from James Lagoon, a 30-m-deep drowned cirque valley adjacent to McCarty Fjord in the Nuka Bay region of Kenai Fjords National Park. A 1790 CE terminal moraine deposited by McCarty Glacier extends across the cirque opening and delimits the lagoon. Acoustic surveys of the lagoon reveal bedrock overlain by deltaic, lacustrine, and marine facies containing beds that indicate past submarine landslides. Lagoon and marsh sediment cores contain coarse sand horizons interbedded with silt and peat, evidence of repeated low-frequency, high-intensity events. The largest of the event beds in the marine cores occurs near the surface and is likely associated with the 1964 Great Alaska Earthquake (moment magnitude 9.2). Trees killed during the 1964 earthquake fringe the coastline and indicate ∼2 m of coseismic subsidence. Radiocarbon ages of five exposed subfossil stumps indicate two pre-1964 subsidence events occurring between 1710 and 1789 and 1078 and 1125 median probability calendar year CE (cal CE). A Sugpiaq culture archaeological site dated to 1565 cal CE existed on the western shore of James Lagoon in the interval between these two events, possibly for proximity to an ice floe harbor seal rookery at McCarty Glacier. Archaeological site elevation above mean high water at James Lagoon and around Nuka Bay is inversely related to the extent of cumulative site erosion caused by coastal submergence during the last two great earthquakes. These combined findings lay the groundwork for future research and provide context to ongoing coastal hazards and their effects on cultural resources. [ABSTRACT FROM AUTHOR]

Subduction, isostatic rebound, and changes in global sea levels, combined with the last glaciation, have shaped the geography of the channels of Western Patagonia. Current archaeological research in this area includes some ten sites that allow us to characterize the occupation of this territory by marine hunter-gatherers. The studied archaeological sites also inform about the various geomorphological changes that the coastline has undergone. Archives dating back six thousand years ago and archaeological contexts yield new insights about the location, distribution, and position of the shoreline and its changes over time. We present a set of data, including new sites and AMS radiocarbon determinations, which supports the hypothesis that landforms have risen or subsided, and provide the bases for a working model in which archaeological ages can inform the chronology of changes in the region's coastal morphology. This paper suggest that human occupations between 6200 and 4400 cal BP recorded on high terraces of the Guiatecas Archipelago indicate higher local sea-levels, while the sites immediately on the waterfront are 2000 years younger. On the other hand, sites younger than 3300 cal BP on the modern coastline of the Chonos archipelago undergo permanent shaping, mainly due to local tectonics affecting vertical movement. Considering previously published and new data provided in this paper, we suggest preliminary uplift rates between 0.57 and 5.42 m/ka for the Guaitecas Archipelago, 0.31–1.48 m/ka for the northern sector of the Chonos Archipelago, and 0.85 m/ka in the central sector. [ABSTRACT FROM AUTHOR]

Although it is generally assumed that understanding the trigger factor leading to the transition from a progressive rock failure toward sudden and rapid events is better to risk management, the ability to identify triggering factors responsible for prehistoric catastrophic rock avalanches is still debated. Here we describe two rock avalanches (Ganqiu and Shuiqiu) in the Cuihua Mountain area of the Qinling Range, China, providing new mapping of rock avalanche source areas and deposits and absolute age constraint from cosmogenic 10Be surface exposure dating. Results reveal that the Ganqiu rock avalanche is controlled by three sets of joints, causing the 380 m high ridge to collapse. Debris filled roughly the entire V-shaped valley and has a width ranging from 250 to 470 m, extending ~1260 m from the base of the cliff. The Shuiqiu rock avalanche was sourced near the summit of Cuihua Mountain from a cliff above 60° that is mainly controlled by inherited fault and joints. The rock mass fell ~250 m as a giant blocky stream across the width of the valley floor, with the deposit extending ~300 m from the base of the cliff. Both events caused the large-scale collapse of ridge crests and developed into high-mobility rock avalanches with long runout. Cosmogenic 10Be surface exposure dating from seven different parts of the deposits revealed nearly coincident ages for both rock avalanches, 10.0 ± 0.9 ka for the Ganqiu rock avalanche and 9.5 ± 1.2 ka for the Shuiqiu rock avalanche. Because this region was not affected by valley glaciation, rock avalanches triggering by paraglacial stress release can be excluded. Moreover, without clear evidence for specific climatic conditions in the Qinling area circa 9–10 ka, a climatic trigger for the Cuihua Mountain rock avalanches is equivocal. Instead, we find coincidence between the concurrent exposure ages and paleoseismic records from the nearby Qinling North Piedmont fault (QNF). This coincidence of ages, combined with the fact that the M w 8.0 1556 CE Huaxian earthquake triggered numerous large rock falls in the Huashan Mountains at the eastern end of the Qinling Range, suggest that a large-magnitude earthquake centered in the middle-east section of QNF at ca. 8–11 ka may have triggered the Ganqiu and Shuiqiu rock avalanches. • Two rock avalanches in the Qinling Range (China) were mapped and dated. • Seven nearly uniform 10Be exposure ages constrains the two rock avalanches to 9–10 ka. • Large-magnitude earthquake is a likely candidate for two rock avalanches triggering in the north Qinling Range. [ABSTRACT FROM AUTHOR]

There is growing evidence that climate-induced melting of large ice sheets has been able to trigger fault reactivation and earthquakes around the migrating ice limit. Even today, the stress due to glacial isostatic adjustment can continue to induce seismicity within the once-glaciated region. Northern Central Europe lies outside the former ice margin and is regarded as a low-seismicity area. However, several historic earthquakes with intensities of up to VII occurred in this region during the past 1200 years. Here we show with numerical simulations that the seismicity can potentially be explained by the decay of the Scandinavian ice sheet after the Weichselian glaciation. Combination of historic earthquake epicenters with fault maps relates historic seismicity to major reverse faults of Late Cretaceous age. Mesozoic normal faults remained inactive in historic times. We suggest that many faults in northern Central Europe are active during postglacial times. This is a novelty that sheds new light on the distribution of postglacial faulting and seismicity. In addition, we present the first consistent model that can explain both the occurrence of deglaciation seismicity and the historic earthquakes in northern Central Europe. [ABSTRACT FROM AUTHOR]

Abstract: Event Layers in Neoproterozoic cap carbonates of Brazil's southwestern Amazon Craton record post-Marinoan synsedimentary seismicity. The 35 m-thick cap carbonates overlie glaciogenic sediments related to the Marinoan glaciation (635 Ma) and are comprised of two units: the lower cap consists of dolomite (∼15 m thick) and the upper cap is limestone (∼25 m thick). The cap dolomite includes pinkish crystalline dolostone with even parallel lamination, stratiform stromatolites, eventual tube structures and megaripple bedded peloidal dolostone interpreted as shallow (euphotic) platform deposits. The cap limestone onlaps the cap dolomite and consists of red marl, gray to black bituminous lime mudstone, bituminous shale with abundant calcite crystal fans (pseudomorphs after aragonite) and even parallel lamination interpreted as moderately deep to deep platform deposits. Five successive events of synsedimentary deformation were recognized in the cap carbonates exposed at Mirassol d'Oeste and Tangará da Serra, in Central Brazil: Event 1 – large to small-scale load cast structures in the contact between dolostones and glaciogenic sediments; Event 2 – stromatolitic lamination truncated by tube structures; Event 3 – vertical to subvertical fractures and faults, and large-scale synclines and anticlines with chevron folds; Event 4 – conglomerate and breccia filling neptunian dykes limited by undeformed beds; and Event 5 – slump and sliding deposits found only in the upper part of the cap limestone. Event 1 was produced by hydroplastic dynamics likely induced by isostatic rebound during ice cap melting in the final stages of the Marinoan glaciation. Events 2 and 5 are autocyclic in nature, and related to depositional processes. Event 2 is linked to fluid and methane escape from organic degradation of microbial mats and domes that formed tubestones; Event 5 is associated to collapse and sliding/slumping in the platform and slope. The reliable orientations of synsedimentary faults, and fractures and folds of events 3 and 4 are consistent with regional extensional tectonics associated with earthquakes that triggered sediment deformation. The 200 km that separate the occurrences of cap carbonates suggest that important seismic events took place during the early Ediacaran in the southern Amazon Craton. [Copyright &y& Elsevier]

Strong earthquakes could serve as a trigger for glacier detachment and associated ice–rock avalanches. The 1988 Tsambagarav earthquake (M = 6.4) initiated collapse of part of the glacier tongue and a further ice–rock avalanche with an abnormal 5 km long path in Zuslan valley, Tsambagarav ridge (Mongolian Altai). Early documentation of surface effects in 1988, remote sensing and field data gathered 16 and 30 years after this event allowed for the assessment of the seismic impact on a reduction of "damaged" glacier under conditions of global warming as well as estimating topography changes in this arid and seismically active area. Because of the earthquake, the glacier immediately lost 10.4 % of its area (0.1 km2 of tongue surface). Additionally, 56% of its area was lost during 1988–2015, shrinking much faster than neighboring glaciers of similar size and exposition. Collapse of snow–ice cornice in the accumulation zone could play a key role in rapid acceleration of the detached ice block and abnormally long path of the ice–rock avalanche. A large amount of debris material provided more than 16 years of ice melting. Downstream, the valley avalanche debris cover repeats the topography of underlying Pleistocene moraines, which should be considered in regional paleogeographical reconstructions. [ABSTRACT FROM AUTHOR]

The comparison of seismological materials with the front boundary of the latest continental glaciation has shown that all revealed really tectonic earthquakes occur exclusively in the occurrence area of a thick cover of this glaciation. The thickness of the glacier at a distance of about 50-100 km from its front could have reached 1 km, and the amplitude of glacioisostatic lowering and subsequent uplifts could have reached 0.3 km. The total amplitude of these movements, which were taking place during 20 thousand years, is comparable with the amplitudes of vertical neotectonic movements, which were taking place during 35-37 million years and on the average were three orders of magnitude more intense than neotectonic movements. With such amplitudes and speeds of vertical glacioisostatic movements, it looks quite plausible that the buried rupture zones could be revived recently (including in Holocene) with block movements of crystalline basement with an amplitude of a few tens of meters. This explains the localization of modern seismicity, which is a hazard to construction, within the occurrence domain of the latest glacial shield. The steady decline in the velocities of glacioisostatic movements after the retreat of the latest glaciation was accompanied by a decrease in the general seismic activity. Against this background, pulsations of seismic activity were recorded in the historical period, the latest phase of its intensification being recorded in the late XX-early XXI century. The general trend toward a decrease in seismotectonic activity in Holocene does not allow the characteristics of early Holocene and more ancient seismodislocations to be used to characterize modern seismicity. [ABSTRACT FROM AUTHOR]

During the last stages of the Weichselian glaciation (ca. 9,000-15,000 years B.P.), reduced ice loads and glacially affected stress fields resulted in active faulting in Fennoscandia with fault scarps up to 160 km long and up to 30 m high. These postglacial (PG) faults are usually SE dipping, SW-NE oriented thrusts, and represent reactivated, pre-existing crustal discontinuities. Postglacial faulting indicates that the glacio-isostatic compensation is not only a gradual viscoelastic phenomenon, but also includes unexpected violent earthquakes, suggestively larger than other known earthquakes in stable continental regions. We explore here possibilities and benefits for investigating, via scientific drilling, the characteristics of postglacial faults in northern Fennoscandia, including their structure and rock properties, present and past seismic activity and state of stress, as well as hydrogeology and associated deep biosphere. The research is anticipated to advance science in neotectonics, hydrogeology and deep biosphere studies, and provide important information for nuclear waste disposal, petroleum exploration on the Norwegian continental shelf and studies of mineral resources in PG fault areas. [ABSTRACT FROM AUTHOR]