Subjects -> EARTH SCIENCES (Total: 771 journals)     - EARTH SCIENCES (527 journals)    - GEOLOGY (94 journals)    - GEOPHYSICS (33 journals)    - HYDROLOGY (29 journals)    - OCEANOGRAPHY (88 journals) EARTH SCIENCES (527 journals)            First | 1 2 3
 Showing 401 - 371 of 371 Journals sorted alphabetically Physical Geography       (Followers: 8) Physical Science International Journal Physics in Medicine & Biology       (Followers: 15) Physics of Life Reviews       (Followers: 1) Physics of Metals and Metallography       (Followers: 18) Physics of Plasmas       (Followers: 10) Physics of the Earth and Planetary Interiors       (Followers: 34) Physics of the Solid State       (Followers: 4) Physics of Wave Phenomena Physics World       (Followers: 18) Physik in unserer Zeit       (Followers: 9) Pirineos Planet       (Followers: 4) Plasma Physics and Controlled Fusion       (Followers: 6) Plasma Physics Reports       (Followers: 7) Polar Record       (Followers: 2) Positioning       (Followers: 4) Pramana       (Followers: 13) Precambrian Research       (Followers: 7) Preview Proceedings of the Geologists' Association       (Followers: 6) Proceedings of the Linnean Society of New South Wales       (Followers: 2) Proceedings of the Yorkshire Geological Society       (Followers: 1) Progress in Earth and Planetary Science       (Followers: 15) Pure and Applied Geophysics       (Followers: 12) Quarterly Journal of Engineering Geology and Hydrogeology       (Followers: 4) Quaternary Quaternary Australasia Quaternary Geochronology       (Followers: 8) Quaternary International       (Followers: 14) Quaternary Research       (Followers: 19) Quaternary Science Advances Quaternary Science Reviews       (Followers: 26) Radiocarbon       (Followers: 12) Remote Sensing       (Followers: 57) Remote Sensing Applications : Society and Environment       (Followers: 9) Remote Sensing in Earth Systems Sciences       (Followers: 5) Remote Sensing Letters       (Followers: 45) Remote Sensing Science       (Followers: 29) Rendiconti Lincei Reports on Geodesy and Geoinformatics       (Followers: 8) Reports on Mathematical Physics       (Followers: 2) Research & Reviews : Journal of Space Science & Technology       (Followers: 18) Resource Geology       (Followers: 6) Resources, Environment and Sustainability       (Followers: 1) Results in Geochemistry Results in Geophysical Sciences Reviews in Mineralogy and Geochemistry       (Followers: 4) Reviews of Modern Physics       (Followers: 31) Revista Cerrados Revista de Ciências Exatas Aplicadas e Tecnológicas da Universidade de Passo Fundo : CIATEC-UPF Revista de Ingenieria Sismica Revista de Investigaciones en Energía, Medio Ambiente y Tecnología Revista de la Academia Colombiana de Ciencias Exactas, Físicas y Naturales Revista de Teledetección Revista Geológica de Chile Revue Française de Géotechnique Rock Mechanics and Rock Engineering       (Followers: 7) Rocks & Minerals       (Followers: 3) Russian Geology and Geophysics       (Followers: 2) Russian Journal of Mathematical Physics Russian Journal of Pacific Geology Russian Physics Journal       (Followers: 1) Science China Earth Sciences       (Followers: 3) Science News       (Followers: 11) Science of Remote Sensing       (Followers: 7) Scientific Annals of Stefan cel Mare University of Suceava. Geography Series Scientific Journal of Earth Science       (Followers: 1) Scientific Reports       (Followers: 85) Sedimentary Geology       (Followers: 20) Sedimentology       (Followers: 15) Seismic Instruments       (Followers: 1) Seismological Research Letters       (Followers: 12) Soil Dynamics and Earthquake Engineering       (Followers: 14) Soil Security       (Followers: 3) Solid Earth       (Followers: 5) Solid Earth Discussions       (Followers: 1) Solid Earth Sciences       (Followers: 1) South African Journal of Geomatics       (Followers: 2) Standort - Zeitschrift für angewandte Geographie       (Followers: 2) Stratigraphy and Geological Correlation       (Followers: 2) Studia Geophysica et Geodaetica       (Followers: 1) Studia Geotechnica et Mechanica Studia Universitatis Babes-Bolyai, Geologia Survey Review       (Followers: 6) Surveys in Geophysics       (Followers: 3) Swiss Journal of Palaeontology       (Followers: 4) Tectonics       (Followers: 15) Tectonophysics       (Followers: 24) Tellus A       (Followers: 21) Tellus B       (Followers: 20) Terra Latinoamericana Terra Nova       (Followers: 5) The Compass : Earth Science Journal of Sigma Gamma Epsilon The Holocene       (Followers: 16) The Leading Edge       (Followers: 1) Transportation Infrastructure Geotechnology       (Followers: 8) Turkish Journal of Earth Sciences UD y la Geomática Unconventional Resources Underwater Technology: The International Journal of the Society for Underwater       (Followers: 1) Universal Journal of Geoscience Unoesc & Ciência - ACET Vadose Zone Journal       (Followers: 5) Volcanica Water       (Followers: 10) Water International       (Followers: 19) Water Resources       (Followers: 21) Water Resources Research       (Followers: 94) Watershed Ecology and the Environment Weather, Climate, and Society       (Followers: 15) Wiley Interdisciplinary Reviews - Climate Change       (Followers: 33) World Environment       (Followers: 1) Yearbook of the Association of Pacific Coast Geographers       (Followers: 2) Yugra State University Bulletin       (Followers: 1) Zeitschrift der Deutschen Gesellschaft für Geowissenschaften       (Followers: 3) Zeitschrift für Geomorphologie       (Followers: 5) Zitteliana Землеустрій, кадастр і моніторинг земель       (Followers: 1)

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 Progress in Earth and Planetary ScienceJournal Prestige (SJR): 1.349 Citation Impact (citeScore): 3Number of Followers: 15     Open Access journal ISSN (Online) 2197-4284 Published by SpringerOpen  [228 journals]
• The pteropod species Heliconoides inflatus as an archive of late
Pleistocene to Holocene environmental conditions on the Northwest Shelf of
Australia

• Abstract: Abstract There is growing interest in the use of pteropods as potential archives of past changes in ocean chemistry. However, pteropods have rarely been used in studies of millennial-scale sedimentary records, especially in shallow-marine environments. This study obtained core data for the last 16 kyr from the Northwest Shelf of Australia (NWS). Changes in the carbonate saturation state were assessed based on the carbon isotope ratios (δ13C) of shells and the Limacina dissolution index (LDX) measured on the planktonic pteropod species Heliconoides inflatus. In addition, the calcification depth of the pteropods was estimated based on oxygen isotope values (δ18O) of pteropod shells and seawater. Our findings indicate that H. inflatus calcifies at a depth of 95–140 m. This confirms that H. inflatus records a shallow-marine signal on the NWS. The δ13C values of the pteropods record a notable decrease in carbonate ion concentrations after 8.5 ka. This decrease is associated with the post-glacial onset of humid conditions on the NWS. The studied pteropod shells are pristine throughout the 16 kyr section and have low LDX values. Therefore, the LDX proxy appears to lack the sensitivity to be applicable in this highly supersaturated, shallow-marine environment. Until this study, proxies derived from H. inflatus have been exclusively utilized in open-marine settings. Our results indicate that the δ13C values of H. inflatus also represent a useful proxy for carbonate ion concentrations in shallow-marine environments.
PubDate: 2022-10-01

• DigitSeis: software to extract time series from analogue seismograms

• Abstract: Abstract A vast amount of analogue seismograms recorded between the end of the nineteenth century and late twentieth century are often inaccessible for seismological research since they are not available as digital time series. This manuscript describes freely available software, DigitSeis, that takes a digital image of an analogue seismic record and returns waveforms either as a function of their x-y position on the image or as time–amplitude information. The overall structure and approach of the software are provided along with how they have evolved over different versions. The effectiveness of the software is demonstrated with three examples. The first example is a long-period east–west seismogram recorded at the Harvard Seismographic Observatory on photographic paper in May of 1938, which contains signals associated with a magnitude 7.7 earthquake that occurred off the coast of Northern Ibaraki, Japan. The second example is an analysis of a 35-mm microfilm copy of the short-period vertical seismogram recorded at Tucson, Arizona, on July 16, 1945, that shows blast signals from the first nuclear bomb detonation. The final example uses a 70 mm microfiche image of a long-period north–south seismogram recorded at College, Alaska in December of 1966, which shows a pair of earthquakes with nearly identical waveforms. The software is, by no means, perfect, and discussion of its limitations such as the compatibility with pen- and Develocorder-type seismograms is included, as well as comments about challenges of incorporating machine learning into the digitization process.
PubDate: 2022-10-01

• Exploration of spatial and temporal variability of rainfall and their
impact on rice production in Burma in 1901–1939 during the colonial
period

• Abstract: Abstract Climate is one of the main factors for rice crop growth. Understanding the relationship between climate variability and rice production during the period from 1901 to 1939 in Burma can give a clear picture of the impact of climate variability on rice yield since there were fewer human interventions on the catchment and almost no use of chemical fertilizer or high-yielding rice varieties at that time. However, the quantitative analysis of climate variability and its impact on rice production has not yet been paid sufficient scientific attention for the historic period. First, the changing trends of rainfall and rice yield between 1901 and 1939 were analyzed, including the effect of rainfall variability on rice production from multiple perspectives regarding rainfall characteristics, such as seasonal rainfall, various rainfall indices, rainfall anomalies, and monthly rainfall variability. Then, the relationship between rice yield and rainfall was investigated using multiple regression analysis to show how rainfall spatial and temporal variabilities have influenced rice yield and production, including essential factors that affected rice yield in each Burma district. The historical development of rice production in Burma during the period was also explored. Our findings indicate that not only the annual variability of rainfall, but also its monthly variability within a particular year likely influenced rice production. Excessive rainfall in the early or middle stage of crop growth or less during the early-middle or latter half of crop growth possibly caused the rice yield reduction in Burma during the colonial period. Furthermore, the results indicated that although rainfall anomalies widely differed from period to period, rice yield anomalies clearly showed the distinction of periods with higher or lower rice yields than average rice yield. Mostly higher than average rice yield was observed before 1910 in the Coastal Zone and before 1918 in the Delta, Dry, and Hilly Zones. The results of this study imply that selected rainfall indices could affect rice yield, positively or negatively, including the varied magnitude of their effects from one district to another, depending on climatic zones and agricultural ecosystems.
PubDate: 2022-09-07

• Precision and convergence speed of the ensemble Kalman filter-based
parameter estimation: setting parameter uncertainty for reliable and
efficient estimation

• Abstract: Abstract Determining physical process parameters in atmospheric models is critical to obtaining accurate weather and climate simulations; estimating optimal parameters is essential for reducing model error. Recently, automatic parameter estimation using the ensemble Kalman filter (EnKF) has been tested instead of conventional manual parameter tuning. To maintain uncertainty for the parameters to be estimated and avoid filter divergence in EnKF-based methods, some inflation techniques should be applied to parameter ensemble spread (ES). When ES is kept constant through the estimation using an inflation technique, the precision and convergence speed of the estimation vary depending on the ES assigned to estimated parameters. However, there is debate over how to determine an appropriate constant ES for estimated parameters in terms of precision and convergence speed. This study examined the dependence of precision and convergence speed of an estimated parameter on the ES to establish a reliable and efficient method for EnKF-based parameter estimation. This was carried out by conducting idealized experiments targeting a parameter in a cloud microphysics scheme. In the experiments, there was a threshold value for ES where any smaller values did not result in any further improvements to the estimation precision, which enabled the determination of the optimal ES in terms of precision. On the other hand, the convergence speed accelerates monotonically as ES increases. To generalize the precision and convergence speed, we approximated the time series of parameter estimation with a first-order autoregression (AR(1)) model. We demonstrated that the precision and convergence speed may be quantified by two parameters from the AR(1) model: the autoregressive parameter and the amplitude of random perturbation. As the ES increases, the autoregressive parameter decreases, while the random perturbation amplitude increases. The estimation precision was determined based on the balance between the two values. The AR(1) approximation provides quantitative guidelines to determine the optimal ES for the precision and convergence speed of the EnKF-based parameter estimation.
PubDate: 2022-09-06

• Reply to “Comment on ‘Soil salinity assessment by using near-infrared
channel and Vegetation Soil Salinity Index derived from Landsat 8 OLI
data: a case study in the Tra Vinh Province, Mekong Delta, Vietnam’ by
Kim-Anh Nguyen, Yuei-An Liou, Ha-Phuong Tran, Phi-Phung Hoang and
Thanh-Hung Nguyen”

• Abstract: Abstract The Vietnamese Mekong Delta has been devastatingly impacted by climate change coupled with sea level rise and natural hazards. As a result, salinity intrusion has become a pressing issue in the coastal provinces of the Mekong Delta in recent years. This environmental problem has called a great attention from the global scientists as demonstrated by the paper Nguyen et al. (Prog Earth Planet Sci 7:1, 2020. 10.1186/s40645-019-0311-0) “Soil salinity assessment by using an indicator derived from Landsat 8 OLI data: A case study in the Tra Vinh, Mekong Delta, Vietnam” (reached 27 k accesses as of July 31, 2022). Recently, Silvestri et al. (PEPS, 2022) have commented on Nguyen et al. (2020) article with three main points highlighted: (1) Within the coastal portion of the Mekong Delta, extensively ponded due to widespread shrimp farming, about 90% of Landsat 8 pixels are fully or partially covered by water so that Landsat 8 OLI spatial resolution is not suitable to distinguish between ponded and non-ponded areas; (2) The decreased near-infrared (NIR) reflectance ascribed to increased soil salinity is instead due to the presence of water in Landsat 8 mixed pixels; and (3) NIR reflectance is equally reduced independently of whether the water ponding area is salt or freshwater. We appreciate Silvestri et al. (2022) for their correspondence regarding our 2020 article (Nguyen et al. 2020) where we showed the capacity of using freely accessible Landsat 8 OLI image for the rapid soil salinity detection at the top soil layer in the agricultural land that is of valuable information for agricultural activities. We conducted field survey and collected the soil samples during the dry season at different agricultural soil types. Notably, the soil samples were collected at the same time with the satellite passing over the study area. The soil salinity derived from Landsat 8 is in line with the analysis from in situ data and consistent with the findings of previous studies. Importantly, two points are stressed in this reply: (1) The goal of our study is to utilize the freely accessible data source with rapid method of mapping soil salinity to investigate the salinity in the agricultural land, but not in the water body. Therefore, it has been a serious mistake to state that 90% of Landsat 8 pixels are fully or partially covered by water as claimed in Silvestri et al. (2022); and (2) The Tra Vinh Province has recorded the highest salinity level normally in March or April every year when the rainfall exhibits the lowest of the year, and at this time, most of the water in the river/canal is affected by saline intrusion. Thus, it is advised that Silvestri et al. (2022) should use the images acquired in March or April rather than random months.
PubDate: 2022-09-02

• Comment on “Soil salinity assessment by using near-infrared channel and
Vegetation Soil Salinity Index derived from Landsat 8 OLI data: a case
study in the Tra Vinh Province, Mekong Delta, Vietnam” by Kim-Anh
Nguyen, Yuei-An Liou, Ha-Phuong Tran, Phi-Phung Hoang and Thanh-Hung
Nguyen

• Abstract: Abstract Nguyen et al. (Prog Earth Planet Sci 7:1, 2020. https://doi.org/10.1186/s40645-019-0311-0) suggest that Landsat 8 OLI can be used to map and monitor soil salinity in the coastal zone of the Mekong River Delta. The authors use empirical correlations between the near-infrared (NIR) band, or vegetation indexes containing the NIR band, and soil salinity. We show that within the coastal portion of the Mekong Delta, extensively ponded due to widespread shrimp farming, about 90% of Landsat 8 pixels are fully or partially covered by water. We then find that, due to strong NIR radiation absorption, NIR reflectance from ponded pixels decreases linearly with increasing water percentage cover, while no significant correlation is found between reflectance and soil salinity. Through detailed new analyses, we conclude that NIR reflectance attenuation cannot be ascribed to vegetation stress caused by soil salinity, but rather to the presence of water ponds. We also show that a similar behavior exists in ponded freshwater inland areas, confirming that the NIR absorption exerted by water is independent of salinity.
PubDate: 2022-09-02

• Characterization of water masses around the southern Ryukyu Islands based
on isotopic compositions

• Abstract: Abstract We investigated the water-mass structure on the Okinawa Trough and Pacific sides of the southern Ryukyu Island Arc (Yonaguni, Iriomote, and Ishigaki subareas) using the Nd isotope composition (143Nd/144Nd ratios; expressed as εNd values) of benthic foraminiferal tests in surface sediments, which reflect bottom-water composition, along with hydrogen and oxygen isotope compositions (δD and δ18O values, respectively) and physical properties (temperature and salinity) of seawater. The Okinawa Trough side has lower εNd values than the Pacific side due to continental/island material inputs characterized by relatively low εNd values. Moreover, within the Okinawa Trough, other processes control the Nd behavior of seawater and primarily affect the Yonaguni and Iriomote subareas, as follows. (1) Surface and subsurface waters are influenced by Taiwanese river discharge combined with temporospatial variations in oceanographic conditions including Kuroshio Current meandering. (2) Intermediate water is characterized by low εNd values (down to − 8.2), possibly attributable to sediment plumes and turbiditic fluxes. (3) The εNd values of bottom water indicate upwelling and vertical mixing, with composition therefore being similar to those of intermediate water. The εNd profiles are better defined on the Pacific side. High εNd values occur in surface and subsurface (< 300 m depth, potential density < 25.0 kg m−3) waters, and low values (down to − 7.0) occur in subsurface–core-intermediate water (400–600 m depth, 26–27 kg m−3). εNd values increase slightly to − 4.0 below 750 m depth and remain constant down to about 2000 m depth, below which deep water shows a slight decrease in εNd values. Intermediate and bottom/deep waters are distinguished from upper layers by their lower δD and δ18O values.
PubDate: 2022-08-17

• Experiments on seepage-triggered cliff landslides using cohesive wet sand

• Abstract: Abstract Unsaturated wet sand possesses capillary cohesion that is lost when it becomes saturated. Thus, it can form a cliff, but a slide may be triggered upon saturation. Here we conduct cliff landslide experiments using cohesive wet sand where the groundwater seeps in from the hydraulic head $$h_\mathrm{w}$$ located at the rear of a cliff (height H) and vary these parameters. Importantly, we measure both the total stress $$\sigma$$ and pore water pressure u to obtain the effective stress $$\sigma ' = \sigma - u$$ . The experiments show that for a fixed H ( $$\simeq 20$$ cm), a slide is triggered when the $$h_\mathrm{w}$$ exceeds a critical level. The slide occurs nearly simultaneous or after the groundwater seeps out from the cliff toe and the vertical velocity increases approximately exponentially during the slide. As $$h_\mathrm{w}$$ rises, 2 slides are triggered that progress downslope, and for the highest $$h_\mathrm{w}$$ , the whole cliff is pushed forward after the first slide. On the other hand, when the H is high, the slide becomes deep seated. The time needed for the water to seep out from the cliff toe decreases with the $$h_\mathrm{w}$$ and increases with the H, as modeled by a permeable flow with a permeability that decreases with the $$\sigma '$$ . The $$\sigma _\mathrm{z}$$ (vertical) is initially uneven and deviates from the lithostatic value by arching. For tall cliffs, the $$\sigma _\mathrm{z}$$ near the cliff toe falls precipitously soon after the seepage starts prior to the rise in u, indicating that a stress redistribution occurred as the wet sand loses cohesion and slip plane develops. This also indicates the efficacy of $$\sigma$$ measurement because the changes are detected before the groundwater arrives. A stability analysis that models the drop in cohesion and a rise in u explains the cliff becoming unstable with $$h_\mathrm{w}$$ and the slide becoming deep seated with H. However, it overestimates the factor of safety $$F_\mathrm{s}$$ because it does not include the capillary rise and the fall in $$\sigma _\mathrm{z}$$ .
PubDate: 2022-08-12

• Toward a long-term atmospheric CO2 inversion for elucidating natural
carbon fluxes: technical notes of NISMON-CO2 v2021.1

• Abstract: Abstract Accurate estimates of the carbon dioxide (CO2) fluxes at the earth’s surface are imperative for comprehending the carbon cycle mechanisms and providing reliable global warming predictions. Furthermore, they can also provide valuable science-based information that will be helpful in reducing human-induced CO2 emissions. Inverse analysis is a prominent method of quantitatively estimating spatiotemporal variations in CO2 fluxes; however, it involves a certain level of uncertainty and requires technical refinement, specifically to improve the horizontal resolution so that local fluxes can be compared with other estimates made at the regional or national level. In this study, a novel set of inversion schemes was incorporated into a state-of-the-art inverse analysis system named NISMON-CO2. The introduced schemes include a grid conversion, observational weighting, and anisotropic prior error covariance, the details of which are described. Moreover, pseudo-observation experiments were performed to examine the effect of the new schemes and to assess the reliability of NISMON-CO2 for long-term analysis with practical inhomogeneous observations. The experiment results evidently demonstrate the advantages of the grid conversion scheme for high-resolution flux estimates (1° × 1°), with notable improvements being achieved through the observational weighting and anisotropic prior error covariance. Furthermore, the estimated seasonal and interannual variations in regional CO2 fluxes were confirmed to be reliable, although some potential bias in terms of global land–ocean partitioning was observed. Thus, these results are useful for interpreting the flux variations that result from real-observation inverse analysis by NISMON-CO2 ver. 2021.1.
PubDate: 2022-08-11

• Assessing and projecting surface air temperature conditions required to
sustain permafrost in Japan

• Abstract: Abstract Permafrost covers a wide area of the Northern Hemisphere, including high-altitude mountainous areas and even at mid-latitudes. There is concern that the thawing of mountain permafrost can cause slope instability and substantially impact alpine ecosystems, and because permafrost in mountainous areas is difficult to observe, detailed analyses have not been performed on its current distribution and future changes. Although previous studies have observed permafrost only at a limited number of points in Japan (e.g., Daisetsu Mountains, Mt. Fuji, and Mt. Tateyama in the Northern Japan Alps), we show that permafrost potentially exists in nine domains in Japan (Daisetsu Mountains, Mt. Fuji, Northern and Southern Japan Alps, Hidaka Mountains, Mt. Shiretokodake, Sharidake, Akandake, and Yotei). In the Daisetsu Mountains and Mt. Fuji, the environmental conditions required for maintaining at least some permafrost are projected to remain in the future if a decarbonized society is achieved (RCP2.6 or RCP4.5). However, if greenhouse gas emissions continue to increase (RCP8.5), the environmental conditions required for sustaining permafrost are projected to disappear in the second half of the twenty-first century. In other domains, the environmental conditions required for maintaining permafrost are either projected to disappear in the next ten years (Hidaka Mountains, Northern Japan Alps) or they have almost disappeared already (Southern Japan Alps, Mt. Shiretokodake, Sharidake, Akandake, and Yotei). Our projections show that climate change has a tremendous impact on Japan's mountain permafrost environment and suggests the importance of monitoring the mountain environment and considering measures for adapting to future climate change.
PubDate: 2022-08-02

• Geomorphological processes and their connectivity in hillslope, fluvial,
and coastal areas in Bangladesh: A review

PubDate: 2022-07-25

• Long-chain alkenones in the Shimosa Group reveal palaeotemperatures of the
Pleistocene interglacial Palaeo-Tokyo Bays

• Abstract: The Shimosa Group, a Middle- to Late-Pleistocene sedimentary succession, has been the focus of stratigraphic attention because it lies beneath the Tokyo metropolitan area of central Japan. It is also of palaeoclimatic significance because it contains important interglacial marine strata of the past 450,000 years. Because the marine strata of the Shimosa Group were formed in the shallow inner bay known as the Palaeo-Tokyo Bay, rare occurrences of planktonic foraminifera make it difficult to quantitatively reconstruct the palaeo-sea surface temperatures (SSTs). Here, we extracted long-chain alkenones (LCAs) from the core GS-UR-1 penetrating the Shimosa Group to Marine Isotope Stage (MIS) 11. We found that the alkenone unsaturation ratio appears to reflect the SST of the Palaeo-Tokyo Bay formed during the peaks of MISs 5e, 7e, 9, and 11, which was consistent with the inflowing water mass changes inferred from the benthic foraminiferal assemblages. The palaeo-SSTs during each interglacial period were 2–3 °C higher than the pre-industrial levels of Tokyo Bay and seemed to reach a level similar to that of the Holocene thermal maximum. The findings of this study demonstrate that the LCA-based proxy, which has not before been utilised in studies on the Shimosa Group, has strong potential to provide palaeoceanic and stratigraphic information.
PubDate: 2022-07-22

• Hadean/Eoarchean tectonics and mantle mixing induced by impacts: a
three-dimensional study

• Abstract: Abstract The timing of the onset of plate tectonics on Earth remains a topic of strong debate, as does the tectonic mode that preceded modern plate tectonics. Understanding possible tectonic modes and transitions between them is also important for other terrestrial planets such as Venus and rocky exoplanets. Recent two-dimensional modelling studies have demonstrated that impacts can initiate subduction during the early stages of terrestrial planet evolution—the Hadean and Eoarchean in Earth’s case. Here, we perform three-dimensional simulations of the influence of ongoing multiple impacts on early Earth tectonics and its effect on the distribution of compositional heterogeneity in the mantle, including the distribution of impactor material (both silicate and metallic). We compare two-dimensional and three-dimensional simulations to determine when geometry is important. Results show that impacts can induce subduction in both 2-D and 3-D and thus have a great influence on the global tectonic regime. The effect is particularly strong in cases that otherwise display stagnant-lid tectonics: impacts can shift them to having a plate-like regime. In such cases, however, plate-like behaviour is temporary: as the impactor flux decreases the system returns to what it was without impacts. Impacts result in both greater production of oceanic crust and greater recycling of it, increasing the build-up of subducted crust above the core-mantle boundary and in the transition zone. Impactor material is mainly located in the upper mantle, at least at the end of the modelled 500-million-year period. In 2-D simulations, in contrast to 3-D simulations, impacts are less frequent but each has a larger effect on surface mobility, making the simulations more stochastic. These stronger 2-D subduction events can mix both recycled basalt and impactor material into the lower mantle. These results thus demonstrate that impacts can make a first-order difference to the early tectonics and mantle mixing of Earth and other large terrestrial planets, and that three-dimensional simulations are important to obtain less stochastic results, and also to not over- or under-predict the amount of impactor material mixed into the mantle and the time during which a specific tectonic regime acts.
PubDate: 2022-07-12

• Short-wave run-ups of the 1611 Keicho tsunami along the Sanriku Coast

• Abstract: Abstract A tsunami generated by an earthquake that occurred off the east coast of Japan in 1611 was predominantly concentrated along the Sanriku Coast. The 1611 event produced its greatest observed tsunami height at Koyadori, 28.8 m, higher than that produced by other representative tsunamis at the same location such as the 2011 Tohoku and 1896 Meiji Sanriku tsunamis. The characteristics of the source that resulted in the remarkable tsunami height at Koyadori have been widely debated. In this study, we simulated the local intensification mechanism of the 1611 tsunami and derived some key characteristics of the earthquake that produced the intensification at Koyadori based on these results. First, we investigated the topographical inundation characteristics in representative areas on the Sanriku Coast, including Koyadori, by numerical means. By comparing the numerical results with the observed heights for the 1611 tsunami, we found that a simulated tsunami that was dominated by short-wave components yielded a promising reproduction of the observed heights. The development of a local resonance seemed a more likely cause for the observed local intensification at Koyadori than a single-pulse wave. These results suggested that the 1611 earthquake produced a tsunami dominated by short-wave components. Furthermore, the source must have been located far off the Tohoku coast near the Japan Trench axis to have had substantial short-wave components along the Sanriku Coast. Based on these findings, we constructed a source scenario for local intensification by investigating the characteristics of Green’s functions from single-point sources. The scenario involves two separate earthquake sources in shallow crustal areas at the plate interface of the subduction zone, resulting in a moment magnitude of 8.5. The tsunami produced by this source model, which reflected the characteristics of a tsunami earthquake, effectively reproduced the local intensification observed on the Sanriku Coast.
PubDate: 2022-07-06

• Correction to: Seismicity distribution in the Tonankai and Nankai
seismogenic zones and its spatiotemporal relationship with interplate
coupling and slow earthquakes

• PubDate: 2022-06-22

• Climatic zonation of Egypt based on high-resolution dataset using image
clustering technique

• Abstract: Abstract Egypt, a predominantly arid and hyper-arid country, is one of the environmentally most fragile regions of the world. The country became a hot spot for climatic extremes and aridity change in the global warming context. The unavailability of a detailed and reliable climate zonation map is a major hindrance to climatic studies in Egypt. This study attempted to generate a high-resolution climate zone map of Egypt based on a novel image analysis technique. For this purpose, a colored image representing Egypt's composite climatology was developed using three high-resolution (1-km) climate variables: rainfall, maximum temperature and minimum temperature during 1979–2013. A spherical evolution algorithm was used to classify the image into different climate zones. Subsequently, the climate zones representing similar climate distribution were merged to generate the climate map of Egypt. The study revealed that Egypt’s distinguishable climate zones could be recognized when the land area was classified into nine zones using the image analysis technique. The statistical analysis of climate variables of each zone revealed similar climatology only in two pairs of zones. The merging of similar climate zones yielded seven climate zones having distinct climate characteristics. The validation of climate zonation using various statistical tests revealed the robustness of the proposed method in classifying climate. The climate zone map generated in the study can be used as a reference for climate change analysis in Egypt.
PubDate: 2022-06-17

• Fabrication of dense albite aggregates by hot pressing

• Abstract: Abstract Synthetic rocks are used in laboratories to measure the physical and chemical properties of Earth’s constituent minerals in order to understand Earth’s interior. To understand the phenomena in the middle and upper crust, dense aggregates of Na-rich plagioclase are necessary. Therefore, we explored a method of fabricating dense aggregates of albite with low porosities, homogeneous microstructures, the absence of melt and sample sizes larger than a cubic centimetre using hot pressing by solid-state sintering. We conducted multiple experiments in which we varied the particle sizes, the agglomerations of powder, the method of forming, the sintering temperature, and the pressure and duration of the hot pressing. Two particle size fractions of powder, less than two micrometres and less than a few hundred nanometres, were prepared by pulverisation and decantation of natural albite powder. Because fine-grained albite powder seems to agglomerate easily, a technique to dry and disperse the powder was also developed. Hot pressing was carried out at temperatures of 1000‒1150 °C and pressures of 40‒120 MPa. The following were found to be important in obtaining dense aggregates of albite: (1) powders with a particle size less than a few hundred nanometres; (2) powders are adequately dispersed; and (3) preparation of green bodies by slip casting, which makes hot pressing efficient. A dense albite aggregate can then be fabricated using hot pressing at a temperature of 1080 °C and pressure of 100 MPa by solid-state sintering.
PubDate: 2022-06-11

• Depth profile of frictional properties in the inner Nankai accretionary
prism using cuttings from IODP Site C0002

• Abstract: Abstract We conduct frictional experiments using cuttings collected at Nankai Trough IODP Site C0002 over 980.5–3262.5 mbsf (meters below seafloor) depth interval to better understand the frictional properties through the accretionary prism. The experiments are conducted at the in situ effective normal stresses (9–37 MPa) under brine-saturated conditions, and the slip velocity is abruptly changed in a stepwise manner to either of 0.3, 3, or 33 µm/s after the steady-state friction is reached. The friction coefficient (μ) of the cuttings samples ranges from 0.45 to 0.60, with a slight increase in μ with increasing depth, related to decreasing smectite content. The velocity dependence of friction (a − b) is positive at all depths and ranges from 0.001 to 0.006, which indicates a velocity-strengthening behavior; these values are consistent with relatively homogeneous deformation microstructures. The critical slip distance (Dc) ranges from 0.5 to 123 μm, with relatively large values obtained for the smectite-rich samples. The changes in both the friction coefficient and rate- and state-friction parameters are likely associated with mineralogical change and consolidation with increasing depth. Although all of the cuttings samples collected from Site C0002 exhibit a velocity-strengthening behavior, a slight decreasing trend in a − b with increasing depth indicates either a nearly neutral velocity dependence or a possible transition to velocity-weakening behavior at greater depths, which may be attributed to the occurrence of slow earthquakes in the Nankai accretionary prism.
PubDate: 2022-06-03

• Seismicity distribution in the Tonankai and Nankai seismogenic zones and
its spatiotemporal relationship with interplate coupling and slow
earthquakes

• Abstract: Abstract We conducted seismic tomography to estimate the seismic velocity structure and to evaluate the spatiotemporal distribution of interplate earthquakes of the Kii Peninsula, central Honshu, Japan, where the Tonankai and Nankai megathrusts are located. Microearthquakes were quantitatively detected by using the data from a cable-type seafloor seismic observation network, completed in 2015. Our velocity model was consistent with the previous 2-D active-source surveys, which reported the areal extent of key structures: a high-velocity zone beneath Cape Shionomisaki, a subducted seamount off Cape Muroto, and the subducted Paleo-Zenith Ridge. The absence of any other subducted seamount with the same or larger spatial scale, than the identified key structures, was confirmed. Our velocity model also revealed that there was not a simple relationship between areas of large coseismic slip or strong interplate coupling and areas of high velocity in the overriding plate. Relocated hypocenters widely ranged from the upper plate to within the slab, while the most active region was attributed to the oceanic crust in the aftershock region of 2004 off-Kii earthquake. Compared with the results from the land-based observation network, the accuracy of the focal depth estimation was substantially improved. Furthermore, we identified the seismic activity in the vicinity of the plate boundary and determined 14 locations for interplate seismicity areas. They were primarily distributed in the range of seismogenic zone temperature (150–350 °C) along the plate boundary and were located outside of the strong interplate coupling zone. Several active areas of interplate earthquakes exhibited clustered activity during the periods of slow-slip events, observed and accompanied with shallow very-low-frequency earthquakes. Thus, regular interplate microearthquakes became active at the plate boundary in the conjunction with slow slip. In summary, as regular earthquakes provide a more accurate source location than slow earthquakes and can detect events of smaller magnitude, monitoring such interplate earthquakes may reveal spatiotemporal variations in the stick–slip conditions on the plate boundary.
PubDate: 2022-06-03

• Global polygons for terrain classification divided into uniform slopes and
basins

• Abstract: Abstract Global terrain classification data have been used for various issues related to topography such as the estimation of soil types and of ground vulnerability to earthquakes and the creation of seismic hazard maps. However, due to the resolution of digital elevation models (DEMs), the terrain classification data from previous studies could not discriminate small landforms such as plains at the bottom of narrow valleys and small rises in plains. Owing to the greater regional variation of small landforms, there is trade-off between DEMs of higher resolution and the creation of global geomorphological legends. To address this problem, we first merged regions with similar topographic characteristics using slope gradients and HAND (height above the nearest drainage) calculated by the 90-m-spatial-resolution DEMs interpolated from the multi-error-removed improved-terrain DEM (MERIT DEM), and united the polygons with the unit catchments of the MERIT-Basins dataset, so that the polygons contain calculated terrain measurements (slope gradient, HAND, surface texture, local convexity, sinks) and noise types as attributes, as well as the ID number of the unit catchment. In addition, we performed k-means clustering on the dataset using slope gradient, HAND, and surface texture, which can be combined with the dataset as a simple terrain classification. The clustering results were prepared in 15 and 40 global uniform clusters and 15 and 40 clusters for each basin to understand the global appearance of the terrain and provide zoning data for regional problem-solving. The 15 clusters were prepared to observe the outline of the terrain without any processing, whereas the 40 clusters were prepared to group and reclassify the polygons to create zoning data for each region. This dataset showed improvements in terms of capturing the small rises in plains compared to the authors' previous global terrain classification data. This dataset can be used as a proxy and is expected to contribute to modeling and estimation in various applications that are known to be related to topography. The datasets of this article are available at [https://gisstar.gsi.go.jp/terrain2021/].
PubDate: 2022-06-03

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