An ocean circulation model in <Emphasis Type="Italic">σ</Emphasis>S-<Emphasis Type="Italic">z</Emphasis>-<Emphasis Type="Italic">σ</Emphasis>B hybrid coordinate and its validation

A 3D, two-time-level, σS-z-σB hybrid-coordinate Marine Science and Numerical Modeling numerical ocean circulation model (HyMOM) is developed in this paper. In HyMOM, the σ coordinate is employed in the surface and bottom regions, and the z coordinate is used in the intermediate layers. This method can overcome problems with vanishing surface cells and minimize the unwanted deviation in representing bottom topography. The connection between the σ and z layers vertically includes an expanded “ghost” method and the linear interpolation. The governing equations in the σS-z-σB hybrid coordinate based on the complete Reynolds-averaged Navier-Stokes equations are derived in detail. The two-level time staggered and Eulerian forward and backward schemes, which are of second-order of accuracy, are adopted for the temporal difference in internal and external mode, respectively. The computation of the baroclinic gradient force is tested in an analytic test problem; the errors for two methods in HyMOM, which are relatively large only in the bottom layers, are obviously smaller than those in the pure σ and z models in almost all of the vertical layers. A quasi-global climatologic numerical experiment is constructed to test the simulation performance of HyMOM. With the monthly mean Levitus climatology data as reference, the HyMOM can improve the simulating accuracy compared with its pure z or σ coordinate implementation.     

Limitations of <Emphasis Type="Italic">H</Emphasis>-<Emphasis Type="Italic">κ</Emphasis> stacking: ambiguous results caused by crustal layering

Over the past decade, the H-κ stacking technique of Zhu and Kanamori (J Geophys Res 105:2969–2980, 2000) has become a standard tool to determine the crustal thickness H and the bulk crustal v_P/v_S ratio κ from teleseismic receiver functions. It is obvious that unfavorable noise conditions as well as a complex 3D velocity structure can severely hamper the interpretation of receiver-function data. However, we observe that ambiguities can even arise from a simple 1D layered velocity structure which raises a high potential for misinterpretations. To analyze the feasibility and basic limitations of the H-κ stacking method, we conduct a series of tests based on synthetic data. The impact of different given elementary parameters, related either to the velocity structure or to the data processing, is evaluated in a series of eight individual tests. We deliberately exclude complications such as 3D structural variations and/or noise to show that even a simple 1D velocity structure, involving, e.g., an additional inter-crustal discontinuity, can have significant consequences for the interpretation of the results. However, our modeling suggests that more complex crustal structures may lead to even less reliable results. Additionally, our tests illustrate that time shifts of the maxima in the H-κ domain due to the superposition and merging of individual phases can lead to significantly overestimated v_P/v_S ratios. In general, the depth to the Moho (or other discontinuities of interest) is less significantly affected. Our tests indicate the necessity to accurately check delay times derived from the maxima of the H-κ stacks against corresponding phases in the receiver functions. Repeating the stacking with varied weighting factors and filter ranges can help to reduce the ambiguities and to avoid possible misinterpretation.     

Improved random noise attenuation using <Emphasis Type="Italic">f</Emphasis>−<Emphasis Type="Italic">x</Emphasis> empirical mode decomposition and local similarity

Conventional f?x empirical mode decomposition (EMD) is an effective random noise attenuation method for use with seismic profiles mainly containing horizontal events. However, when a seismic event is not horizontal, the use of f?x EMD is harmful to most useful signals. Based on the framework of f?x EMD, this study proposes an improved denoising approach that retrieves lost useful signals by detecting effective signal points in a noise section using local similarity and then designing a weighting operator for retrieving signals. Compared with conventional f?x EMD, f?x predictive filtering, and f?x empirical mode decomposition predictive filtering, the new approach can preserve more useful signals and obtain a relatively cleaner denoised image. Synthetic and field data examples are shown as test performances of the proposed approach, thereby verifying the effectiveness of this method.     

Atypical soil behavior during the 2011 Tohoku earthquake (<Emphasis Type="Italic">М</Emphasis><Subscript><Emphasis Type="Italic">w</Emphasis></Subscript> = 9)

To understand physical mechanisms of generation of abnormally high peak ground acceleration (PGA; >1g) during the Tohoku earthquake, models of nonlinear soil behavior in the strong motion were constructed for 27 KiK-net stations located in the near-fault zones to the south of FKSH17. The method of data processing used was developed by Pavlenko and Irikura, Pure Appl Geophys 160:2365–2379, 2003 and previously applied for studying soil behavior at vertical array sites during the 1995 Kobe (М _w ?=?6.8) and 2000 Tottori (М _w ?=?6.7) earthquakes. During the Tohoku earthquake, we did not observe a widespread nonlinearity of soft soils and reduction at the beginning of strong motion and recovery at the end of strong motion of shear moduli in soil layers, as usually observed during strong earthquakes. Manifestations of soil nonlinearity and reduction of shear moduli during strong motion were observed at sites located close to the source, in coastal areas. At remote sites, where abnormally high PGAs were recorded, shear moduli in soil layers increased and reached their maxima at the moments of the highest intensity of the strong motion, indicating soil hardening. Then, shear moduli reduced with decreasing the intensity of the strong motion. At soft-soil sites, the reduction of shear moduli was accompanied by a step-like decrease of the predominant frequencies of motion. Evidently, the observed soil hardening at the moments of the highest intensity of the strong motion contributed to the occurrence of abnormally high PGA, recorded during the Tohoku earthquake.     

Flow over a rounded backward-facing step,using a <Emphasis Type="Italic">z</Emphasis>-coordinate model and a <Emphasis Type="Italic">σ</Emphasis>-coordinate model

Homogeneous, nonrotating flow over a backward-facing rounded step is simulated using the 2D vertical version of two general circulation models, a z-coordinate model—the Massachusetts Institute of Technology general circulation model (MITgcm)—and a σ-coordinate model—the Bergen Ocean Model (BOM). The backward-facing step is a well-known testcase since it is geometrically simple but still embodies important flow characteristics such as separation point, reattachment length, and recirculation of the flow. The study compares the core of the two models and uses constant eddy viscosities and diffusivities. The Reynolds numbers ranges from 2·10² to 2·10⁶. The results correspond with previously published results having a relatively stationary separation point and a fluctuating reattachment length due to downslope propagating eddies released from the reattachment zone for Reynolds numbers higher than or equal to 2 · 10⁴. For Reynolds number within the laminar regime, the flow is stationary. The discrepancies between the models increase by enhancing Reynolds numbers. The σ-coordinate model experiences a reduction in eddy sizes with increasing resolution and Reynolds numbers in correspondence with published experiments, while the size of the eddies are independent of the Reynolds number using the MITgcm. Due to mixing generated by the staircase topography, the z-coordinate model gives a better convergence of the separation point and reattachment length compared with the BOM; however, this conclusion might change with the inclusion of a relevant turbulence scheme.     

Evaluation of the dynamic <Emphasis Type="Italic">p</Emphasis>–<Emphasis Type="Italic">y</Emphasis><Subscript>p</Subscript> loops of pile-supported structures on sloping ground

A key issue in the design of pile-supported structures on sloping ground is soil–pile interaction, which becomes more complicated in case of dynamic loading. This study aimed to evaluate the effect of slope on the dynamic behavior of pile-supported structures by performing a series of centrifuge tests. Three models were prepared by varying the slope and soil density of dry sand grounds. The mass supported on 3 by 3 group piles was shaken applying sinusoidal wave with various amplitudes. Test results showed that the location of maximum values and distribution shape of the bending moment below the ground surface varied noticeably with the pile position in the slope case. The relationship between the soil resistance and pile deflection (p–y_p loops) was carefully evaluated by applying the piecewise cubic spline method to fit the measured bending moment curves along piles. It was found that the shape of the p–y_p loops was irregular due to the effect of slope, and immensely influenced by the movement of the unstable zone. In addition, the effect of the pile group in the horizontal case was evaluated by comparing with the previously suggested curves that represent the relationship between the soil resistance and pile–soil relative displacement (p–y curves) to propose the multiplier coefficients.     

<Emphasis Type="Italic">Prochlorococcus</Emphasis> viruses—From biodiversity to biogeochemical cycles

As the dominant primary producer in oligotrophic oceans, the unicellular picocyanobacterium Prochlorococcus is the smallest and most abundant photosynthetic phytoplankton in the world and plays an important role in marine carbon cycling. Cyanophages that infect Prochlorococcus influence the growth, carbon fixation, diversity, evolution, and environmental adaptation of their hosts. Here, we review studies on the isolation, genomics, and phylogenetic diversity of Prochlorococcus viruses and their interactions with Prochlorococcus. We also review the potential effects of Prochlorococcus viruses on biogeochemical cycling in the ocean.     

The seasonal behavior of the <Emphasis Type="Italic">B</Emphasis><Subscript><Emphasis Type="Italic">z</Emphasis></Subscript> daily variations according to the monitoring at the Bishkek geodynamic site (1993–1995)

The algorithm for monitoring the magnetotelluric field has been briefly described, and the experimental data, obtained at the Bishkek geodynamic site, have been analyzed. The regularities in the seasonal behavior of the variations in the field vertical magnetic component have been revealed.     

Simulating CO<Subscript>2</Subscript> transport into the ocean from a CO<Subscript>2</Subscript> lake at the seafloor using a <Emphasis Type="Italic">z</Emphasis>- and a <Emphasis Type="Italic">σ</Emphasis>-coordinate model

The ocean takes up approximately 2 GT carbon per year due to the enhanced CO₂ concentrations in the atmosphere. Several options have been suggested in order to reduce the emissions of CO₂ into the atmosphere, and among these are CO₂ storage in the deep ocean. Topographic effects of dissolution and transport from a CO₂ lake located at 3,000-m depth have been studied using the z-coordinate model Massachusetts Institute of Technology general circulation model (MITgcm) and the σ-coordinate model Bergen ocean model (BOM). Both models have been coupled with the general ocean turbulence model (GOTM) in order to account for vertical subgrid processes. The chosen vertical turbulence mixing scheme includes the damping effect from stable stratification on the turbulence intensity. Three different topographic scenarios are presented: a flat bottom and the CO₂ lake placed within a trench with depths of 10 and 20 m. The flat case scenario gives good correlation with previous numerical studies of dissolution from a CO₂ lake. When topography is introduced, it is shown that the z-coordinate model and the σ-coordinate model give different circulation patterns in the trench. This leads to different dissolution rates, 0.1 μmol cm^− 2 s^− 1 for the scenario of a 20-m-deep trench using BOM and 0.005–0.02 μmol cm^− 2 s^− 1 for the same scenario using the MITgcm. The study is also relevant for leakages of CO₂ stored in geological formations and to the ocean.     

The <Emphasis Type="Italic">M</Emphasis><Subscript><Emphasis Type="Italic">w</Emphasis></Subscript> = 5.8 14 August 2016 middle Sakhalin earthquake on a boundary between Okhotsk and Eurasian (Amurian) plates

An earthquake with the moment magnitude M _w ?=?5.8 occurred in the middle part of the Sakhalin Island, Russian Federation, on 14 August 2016, at 11:17 a.m. UTC. The earthquake source was located west of the Central Sakhalin Fault Zone, which is considered to mark the boundary between the Okhotsk and Eurasian (Amurian) plates. Moment tensor solution of the mainshock as well as the configuration of aftershock cloud suggests that the earthquake was caused by slip on a SW-dipping reverse fault. For the first time for Sakhalin, we have got the felt reports unified in accordance with DYFI. We also analyzed observed PGA values and, based on them, produced shaking maps.     

The ratio between corner frequencies of source spectra of <Emphasis Type="Italic">P</Emphasis>- and <Emphasis Type="Italic">S</Emphasis>-waves—a new discriminant between earthquakes and quarry blasts

This study analyzes and compares the P- and S-wave displacement spectra from local earthquakes and explosions of similar magnitudes. We propose a new approach to discrimination between low-magnitude shallow earthquakes and explosions by using ratios of P- to S-wave corner frequencies as a criterion. We have explored 2430 digital records of the Israeli Seismic Network (ISN) from 456 local events (226 earthquakes, 230 quarry blasts, and a few underwater explosions) of magnitudes Md?=?1.4–3.4, which occurred at distances up to 250 km during 2001–2013 years. P-wave and S-wave displacement spectra were computed for all events following Brune’s source model of earthquakes (1970, 1971) and applying the distance correction coefficients (Shapira and Hofstetter, Teconophysics 217:217–226, 1993; Ataeva G, Shapira A, Hofstetter A, J Seismol 19:389-401, 2015), The corner frequencies and moment magnitudes were determined using multiple stations for each event, and then the comparative analysis was performed.The analysis showed that both P-wave and especially S-wave displacement spectra of quarry blasts demonstrate the corner frequencies lower than those obtained from earthquakes of similar magnitudes. A clear separation between earthquake and explosion populations was obtained for ratios of P- to S-wave corner frequency f ₀(P)/f ₀(S). The ratios were computed for each event with corner frequencies f ₀ of P- and S-wave, which were obtained from the measured f ₀ ^I at individual stations, then corrected for distance and finally averaged. We obtained empirically the average estimation of f ₀(P)/f ₀(S)?=?1.23 for all used earthquakes, and 1.86 for all explosions. We found that the difference in the ratios can be an effective discrimination parameter which does not depend on estimated moment magnitude M _w .The new multi-station Corner Frequency Discriminant (CFD) for earthquakes and explosions in Israel was developed based on ratios P- to S-wave corner frequencies f ₀(P)/f ₀(S), with the empirical threshold value of the ratio for Israel as 1.48.     

Temporal and spatial variations of <Emphasis Type="Italic">δ</Emphasis><Superscript>15</Superscript>N and <Emphasis Type="Italic">δ</Emphasis><Superscript>18</Superscript>O for atmospheric N<Subscript>2</Subscript>O above the oceanic surface from Shanghai to Antarctica

During the 22nd Chinese Antarctic Research Expedition (CHINARE-22), the atmospheric gas samples above the oceanic surface and near the surface were collected on the track for the scientific ship “Xuelong” and on Millor Peninsula of eastern Antarctica, respectively, using the Tedlar gas bags. Every day the sampling times were 10:00 and 22:00 (local time), respectively. In the laboratory, high-precision measurement of the isotopic compositions for N₂O in these gas samples was conducted using Thermo Finnigan MAT-253 Isotopic Mass Spectrometer with a fully automated interface for the pre-GC concentration (PreCon) of trace gases. The temporal and spatial variations of δ ¹⁵N and δ ¹⁸O in atmospheric N₂O were analyzed. The mean δ ¹⁵N and δ ¹⁸O-N₂O values above the oceanic surface were (7.21±0.50)‰ and (44.52±0.52)‰, respectively. From 30°N to Antarctica, the δ ¹⁵N (6.05‰–7.88‰) linearly increased with the rate of about 0.01‰ with the latitude while the δ ¹⁸O (43.05‰–48.78‰) showed a large fluctuation. The δ ¹⁵N negatively correlated with air temperature and N₂O concentration, and slightly positively correlated with δ ¹⁸O. The summertime variations of δ ¹⁵N and δ ¹⁸O-N₂O appeared the same trend on Millor Peninsula of eastern Antarctica. They significantly positively correlated with each other and negatively with N₂O concentration. The δ ¹⁵N and δ ¹⁸O-N₂O at different sites averaged (7.42±0.35)‰ and (44.69±0.49)‰, respectively, slightly higher than those above the oceanic surface, significantly higher than those of atmospheric N₂O in the low-latitude regions of Northern Hemisphere. The predominant factors affecting the spatial variations of δ ¹⁵N and δ ¹⁸O values were also discussed. The isotopic data given in this study can help to investigate the global and regional N₂O budgets. Supported by the National Natural Science Foundation of China (Grant Nos. 40676005 and 40406001)     

The spatiotemporal analysis of the minimum magnitude of completeness <Emphasis Type="Italic">Mc</Emphasis> and the Gutenberg–Richter law <Emphasis Type="Italic">b</Emphasis>-value parameter using the earthquake catalog of Greece

Spatiotemporal mapping the minimum magnitude of completeness Mc and b-value of the Gutenberg–Richter law is conducted for the earthquake catalog data of Greece. The data were recorded by the seismic network of the Institute of Geodynamics of the National Observatory of Athens (GINOA) in 1970–2010 and by the Hellenic Unified Seismic Network (HUSN) in 2011–2014. It is shown that with the beginning of the measurements at HUSN, the number of the recorded events more than quintupled. The magnitude of completeness Mc of the earthquake catalog for 1970–2010 varies within 2.7 to 3.5, whereas starting from April 2011 it decreases to 1.5–1.8 in the central part of the region and fluctuates around the average of 2.0 in the study region overall. The magnitude of completeness Mc and b-value for the catalogs of the earthquakes recorded by the old (GINOA) and new (HUSN) seismic networks are compared. It is hypothesized that the magnitude of completeness Mc may affect the b-value estimates. The spatial distribution of the b-value determined from the HUSN catalog data generally agrees with the main geotectonic features of the studied territory. It is shown that the b-value is below 1 in the zones of compression and is larger than or equal to 1 in the zones dominated by extension. The established depth dependence of the b-value is pretty much consistent with the hypothesis of a brittle–ductile transition zone existing in the Earth’s crust. It is assumed that the source depth of a strong earthquake can probably be estimated from the depth distribution of the b-value, which can be used for seismic hazard assessment.     

<Emphasis Type="Italic">Homo erectus pekinensis’s</Emphasis> age and environment— with discussion on the relationship among<Emphasis Type="Italic">Homo erectos</Emphasis> from Beijing,Nanjing and Chenjiawo

This paper inspects the relationship betweenHomo erectus from Beijing, Nanjing and Chenjiawo on the viewpoint of environmental variations. Pieces of evidence show that Nanjing and ChenjiawoHomo erectus lived in glacial age at the Marine Oxygen Isotope Stage (MIS) 16, whileHomo erectus pekinensis in major interglacial age at MISs 15-13. It is also recovered that the cave deposits in Tangshan, Nanjing, and Zhoukoudian, Beijing, as well as the deposits at theHomo erectus site in Chenjiawo, have undergone some similar development process. All of them originated from early-middle Middle Pleistocene, and have gone through the test of the major glacial age at MIS 16 and the major interglacial period at the paleosol stage S₅. At the same time, they were also closely connected with some environment events, such as the uplift of the Qinghai-Xizang Plateau, the formation of glaciations and the loess accumulations.     

Temporal variations of <Emphasis Type="Italic">δ</Emphasis><Superscript>18</Superscript>O of atmospheric water vapor at Delingha

Oxygen stable isotope of atmospheric water vapor is widely used to study the modern process of climate. Atmospheric water vapor samples were collected at Dlingha, northeast of Tibetan Plateau during the period from July 2005 to February 2006. The variation of δ ¹⁸O and the relationships between δ ¹⁸O and both the temperature and specific humidity are analyzed in this paper. Results show that the seasonal variation of δ ¹⁸O of atmospheric water vapor at Delingha is remarkable with higher δ ¹⁸O in summer and lower δ ¹⁸O in winter. The temporal variation of vapor δ ¹⁸O shows obvious fluctuations, with magnitude of over 37‰ The daily variation of the δ ¹⁸O is highly correlated with air temperature. The relationship between δ ¹⁸O and atmospheric water vapor content is complex. Study shows that δ ¹⁸O of atmospheric water vapor is positively correlated with specific humidity in winter in seasonal scale and inversely correlated with specific humidity in summer rainy period. The δ ¹⁸O values of atmospheric water vapor are lower than those of precipitation at Delingha, and the average difference is 10.7‰ Variations of δ ¹⁸O of atmospheric water vapor is also found to be affected by precipitation events, The model results show that the precipitation effect could have caused the vapor δ ¹⁸O in the raining season to lower by 7% in average in July and August. Supported by the National Natural Science Foundation of China (Grant Nos. 40671043, 40571039 and 40771048) and National Basic Research Program of China (Grant No. 2005CB422002)     

Plasma pressure distribution in the equatorial plane of the Earth’s magnetosphere at geocentric distances of 6–10<Emphasis Type="Italic">R</Emphasis><Subscript><Emphasis Type="Italic">E</Emphasis></Subscript> according to the international THEMIS mission data

The structure of the averaged plasma pressure distribution in the plasma ring around the Earth at geocentric distances of ∼6–10R _E has been determined. The distribution function moments measured on the international THEMIS mission satellites have been used. The plasma pressure distribution in the equatorial plane at 15R _E > X_SM > −15R _E and 15R _E > Y_SM > −15R _E has been statistically studied. The radial dependence of the plasma pressure at the day-night and morning-evening meridians has been analyzed. It has been indicated that the plasma ring around the Earth has a structure, which is close to being azimuthally symmetric. The achieved results have been compared with the pressure distributions obtained previously. It has been indicated that in the overlapping regions, the achieved results agree with the previously obtained data within the pressure determination errors.     

Methods and technique of measurements of ρ<Subscript><Emphasis Type="Italic">k</Emphasis></Subscript> variations by GEOMES-R6 device

Upgrading of the electrical resistance variometer GEOMES-R6 of the Institute of Geophysics of the Poland Academy of Sciences, with enhancement of functional capabilities of the GEOMES assemblage for its application in laboratory measurements on rock samples, has been carried out. The assemblage operation principle, specifications, and theory of operation are given. Results of the assemblage test at measurements on marble sample and concrete model are presented. It is shown that the installation allows long-duration registration of variations of the value ρ _k on high-ohmic samples.     

Significance of <Emphasis Type="Italic">Vibrio</Emphasis> species in the marine organic carbon cycle—A review

The genus Vibrio, belonging to Gammaproteobacteria of the phylum Proteobacteria, is a genetically and ecologically diverse group of heterotrophic bacteria, that are ubiquitous in marine environments, especially in coastal areas. In particular, vibrios dominate, i.e. up to 10% of the readily culturable marine bacteria in these habitats. The distribution of Vibrio spp. is shaped by various environmental parameters, notably temperature, salinity and dissolved organic carbon. Vibriospp. may utilize a wide range of organic carbon compounds, including chitin (this may be metabolized by most Vibrio spp.), alginic acid and agar. Many Vibrio spp. have very short replication times (as short as ~10 min), which could facilitate them developing into high biomass content albeit for relatively short durations. Although Vibriospp. usually comprise a minor portion (typically ~1% of the total bacterioplankton in coastal waters) of the total microbial population, they have been shown to proliferate explosively in response to various nutrient pulses, e.g., organic nutrients from algae blooms and iron (Fe⁺) from Saharan dust. Thus, Vibrio spp. may exert large impacts on marine organic carbon cycling especially in marginal seas. Genomics and related areas of investigation will reveal more about the molecular components and mechanisms involved in Vibrio-mediated biotransformation and remineralization processes.     

Regional Variations of the <Emphasis Type="Italic">ω</Emphasis>-upper Bound Magnitude of GIII Distribution in the Iranian Plateau

The Iranian Plateau does not appear to be a single crustal block, but an assemblage of zones comprising the Alborz—Azerbaijan, Zagros, Kopeh—Dagh, Makran, and Central and East Iran. The Gumbel’s III asymptotic distribution method (GIII) and maximum magnitude expected by Kijko—Sellevoll method is applied in order to check the potentiality of the each seismogenic zone in the Iranian Plateau for the future occurrence of maximum magnitude (M_max). For this purpose, a homogeneous and complete seismicity database of the instrumental period during 1900–2012 is used in 29 seismogenic zones of the examined region. The spatial mapping of hazard parameters (upper bound magnitude (ω), most probable earthquake magnitude in next 100 years (M₁₀₀) and maximum magnitude expected by maximum magnitude estimated by Kijko—Sellevoll method (max M_{K ? S}^max) reveals that Central and East Iran, Alborz and Azerbaijan, Kopeh—Dagh and SE Zagros are a dangerous place for the next occurrence of a large earthquake.