Regional adjustment factors for three NGA-West2 ground-motion prediction equations to be applicable in northern Iran

Ground-motion prediction equations (GMPEs) are essential tools in seismic hazard studies to estimate ground motions generated by potential seismic sources. Global GMPEs which are based on well-compiled global strong-motion databanks, have certain advantages over local GMPEs, including more sophisticated parameters in terms of distance, faulting style, and site classification but cannot guarantee the local/region-specific propagation characteristics of shear wave (e.g., geometric spreading behavior, quality factor) for different seismic regions at larger distances (beyond about 80 km). Here, strong-motion records of northern Iran have been used to estimate the propagation characteristics of shear wave and determine the region-specific adjustment parameters for three of the NGA-West2 GMPEs to be applicable in northern Iran. The dataset consists of 260 three-component records from 28 earthquakes, recorded at 139 stations, with moment magnitudes between 4.9 and 7.4, horizontal distance to the surface projection of the rupture (R _JB) less than 200 km, and average shear-wave velocity over the top 30 m of the subsurface (V _S30) between 155 and 1500 m/s. The paper also presents the ranking results for three of the NGA-West2 GMPEs against strong motions recorded in northern Iran, before and after adjustment for region-dependent attenuation characteristics. The ranking is based on the likelihood and log-likelihood methods (LH and LLH) proposed by Scherbaum et al. (Bull Seismol Soc Am 94: 2164–2185, 2004, Bull Seismol Soc Am 99, 3234–3247, 2009, respectively), the Nash–Sutcliffe model efficiency coefficient (Nash and Sutcliffe, J Hydrol 10:282–290, 1970), and the EDR method of Kale and Akkar (Bull Seismol Soc Am 103:1069–1084, 2012). The best-fitting models over the whole frequency range are the ASK14 and BSSA14 models. Taking into account that the models’ performances were boosted after applying the adjustment factors, at least moderate regional variation of ground motions is highlighted. The regional adjustment based on the Iranian database reveals an upward trend (indicated as high Q factor) for the selected database. Further investigation to determine adjustment factors based on a much richer database of the Iranian strong-motion records is of utmost important for seismic hazard and risk analysis studies in northern Iran, containing major cities including the capital city of Tehran.     

The 2014 Earthquake Model of the Middle East: ground motion model and uncertainties

We summarize the main elements of a ground-motion model, as built in three-year effort within the Earthquake Model of the Middle East (EMME) project. Together with the earthquake source, the ground-motion models are used for a probabilistic seismic hazard assessment (PSHA) of a region covering eleven countries: Afghanistan, Armenia, Azerbaijan, Cyprus, Georgia, Iran, Jordan, Lebanon, Pakistan, Syria and Turkey. Given the wide variety of ground-motion predictive models, selecting the appropriate ones for modeling the intrinsic epistemic uncertainty can be challenging. In this respect, we provide a strategy for ground-motion model selection based on data-driven testing and sensitivity analysis. Our testing procedure highlights the models of good performance in terms of both data-driven and non-data-driven testing criteria. The former aims at measuring the match between the ground-motion data and the prediction of each model, whereas the latter aims at identification of discrepancies between the models. The selected set of ground models were directly used in the sensitivity analyses that eventually led to decisions on the final logic tree structure. The strategy described in great details hereafter was successfully applied to shallow active crustal regions, and the final logic tree consists of four models (Akkar and Ça?nan in Bull Seismol Soc Am 100:2978–2995, 2010; Akkar et al. in Bull Earthquake Eng 12(1):359–387, 2014; Chiou and Youngs in Earthq Spectra 24:173–215, 2008; Zhao et al. in Bull Seismol Soc Am 96:898–913, 2006). For other tectonic provinces in the considered region (i.e., subduction), we adopted the predictive models selected within the 2013 Euro-Mediterranean Seismic Hazard Model (Woessner et al. in Bull Earthq Eng 13(12):3553–3596, 2015). Finally, we believe that the framework of selecting and building a regional ground-motion model represents a step forward in ground-motion modeling, particularly for large-scale PSHA models.     

Proposal of an empirical site classification method based on target simulated horizontal over vertical spectral ratio

Nowadays, most of the site classifications schemes are based on the predominant period of the site as determined from the average horizontal to vertical spectral ratios of seismic motion or microtremor. However, the difficulty lies in the identification of the predominant period in particular if the observed average response spectral ratio does not present a clear peak but rather a broadband amplification or multiple peaks. In this work, based on the Eurocode-8 (2004) site classification, and assuming bounded random fields for both shear and compression waves-velocities, damping coefficient, natural period and depth of soil profile, one propose a new site-classification approach, based on “target” simulated average \( H/V \) spectral ratios, defined for each soil class. Taking advantage of the relationship of Kawase et al. (Bull Seismol Soc Am 101:2001–2014, 2011), which link the \( H/V \) spectral ratio to the horizontal (\( HTF \)) over the vertical (\( VTF \)) transfer functions, statistics of \( H/V \) spectral ratio via deterministic visco-elastic seismic analysis using the wave propagation theory are computed for the 4 soil classes. The obtained results show that \( H/V \) and \( HTF \) have amplitudes and shapes remarkably different among the four soil classes and exhibit fundamental peaks in the period ranges remarkably similar. Moreover, the “target” simulated average \( H/V \) spectral ratios for the 4 soil classes are in good agreement with the experimental ones obtained by Zhao et al. (Bull Seismol Soc Am 96:914–925, 2006) from the abundant and reliable Japanese strong motions database Kik-net, Ghasemi et al. (Soil Dyn Earthq Eng 29:121–132, 2009) from the Iranian strong motion data, and Di Alessandro et al. (Bull Sesismol Soc Am 106:2, 2011.  https://doi.org/10.1785/0120110084) from the Italian strong motion data. In addition to the 4 EC-8 standard soil classes (A, B, C and D), the superposition of the 4 target \( H/V \) reveals 3 new boundary site classes; AB, BC and CD, for overlapping \( V_{s,30} \) ranges when the predominant peak is not clearly consistent with any of the 4 proposed classes. Finally, one proposes a site classification index based on the ratio between the cross-correlation and the mean quadratic error between the in situ \( H/V \) spectral ratio and the “target” one. In order to test the reliability of the proposed approach, data from 139 sites were used, 132 collected from the Kik-net network database from Japan and 7 from Algeria. The site classification success rate per site class are around 93, 82, 89 and 100% for rock, hard soil, medium soil and soft soil, respectively. Zhao et al. (2006) found an average success for the 4 classes of soil close to 60%, similar to what one found in the present study (63%) without considering the new soil classes, but much smaller if one considers them (86%). In the absence of \( V_{s,30} \) data, the proposed approach can be an alternative to site classification.     

Declustering of Iran earthquake catalog (1983–2017) using the epidemic-type aftershock sequence (ETAS) model

The main goal of this article is to decluster Iranian plateau seismic catalog by the epidemic-type aftershock sequence (ETAS) model and compare the results with some older methods. For this purpose, Iranian plateau bounded in 24°–42°N and 43°–66°E is subdivided into three major tectonic zones: (1) North of Iran (2) Zagros (3) East of Iran. The extracted earthquake catalog had a total of 6034 earthquakes (Mw?>?4) in the time span 1983–2017. The ETAS model is an accepted stochastic approach for seismic evaluation and declustering earthquake catalogs. However, this model has not yet been used to decluster the seismic catalog of Iran. Until now, traditional methods like the Gardner and Knopoff space–time window method and the Reasenberg link-based method have been used in most studies for declustering Iran earthquake catalog. Finally, the results of declustering by the ETAS model are compared with result of Gardner and Knopoff (Bull Seismol Soc Am 64(5):1363–1367, 1974), Uhrhammer (Earthq Notes 57(1):21, 1986), Gruenthal (pers. comm.) and Reasenberg (Geophys Res 90:5479–5495, 1985) declustering methods. The overall conclusion is difficult, but the results confirm the high ability of the ETAS model for declustering Iranian earthquake catalog. Use of the ETAS model is still in its early steps in Iranian seismological researches, and more parametric studies are needed.     

Intensity predictive attenuation models calibrated in Mw for metropolitan France

In the framework of the SIGMA project, a study was launched to develop a parametric earthquake catalog for the historical period, covering the metropolitan territory and calibrated in Mw. A set of candidate calibration events was selected corresponding to earthquakes felt over a part of the French metropolitan territory, which are fairly well documented both in terms of macroseismic intensity distributions (SisFrance BRGM-EDF-IRSN) and magnitude estimates. The detailed analysis of the macroseismic data led us to retain only 30 events out of 65 with Mw ranging from 3.6 to 5.8. In order to supplement the dataset with data from larger magnitude events, Italian earthquakes were also considered (11 events posterior to 1900 with Mw?≥?6.0 out of 15 in total), using both the DBMI11 macroseismic database (Locati et al. in Seismol Resour Lett 85(3):727–734, 2014) and the parametric information from the CPTI11 (Rovida et al. in CPTI11, la versione 2011 del Catalogo Parametrico dei Terremoti Italiani Istituto Nazionale di Geofisica et Vulcanologia, Milano, Bologna, 2011.  https://doi.org/10.6092/ingv.it-cpti11). To avoid introducing bias related to the differences in terms of intensity scales (MSK vs. MCS), only intensities smaller than or equal to VII were considered (Traversa et al. in On the use of cross-border macroseismic data to improve the estimation of past earthquakes seismological parameters, 2014). Mw and depth metadata were defined according to the Si-Hex catalogue (Cara et al. in Bull Soc Géol Fr 186:3–19, 2015.  https://doi.org/10.2113/qssqfbull.186.1.3), published information, and to the specific worked conducted within SIGMA related to early instrumental recordings (Benjumea et al. in Study of instrumented earthquakes that occurred during the first part of the 20th century (1905–1962), 2015). For the depth estimates, we also performed a macroseismic analysis to evaluate the range of plausible estimates and check the consistency of the solutions. Uncertainties on the metadata related to the calibration earthquakes were evaluated using the range of available alternative estimates. The intensity attenuation models were developed using a one-step maximum likelihood scheme. Several mathematical formulations and sub-datasets were considered to evaluate the robustness of the results (similarly to Baumont and Scotti in Accounting for data and modeling uncertainties in empirical macroseismic predictive equations (EMPEs). Towards “European” EMPEs based on SISFRANCE, DBMI, ECOS macroseismic database, 2008). In particular, as the region of interest may be characterized by significant laterally varying attenuation properties (Bakun and Scotti in Geophys J Int 164:596–610, 2006; Gasperini in Bull Seismol Soc Am 91:826–841, 2001), we introduced regional attenuation terms to account for this variability. Two zonation schemes were tested, one at the national scale (France/Italy), another at the regional scale based on the studies of Mayor et al. (Bull Earthq Eng, 2017.  https://doi.org/10.1007/s10518-017-0124-8) for France and Gasperini (2001) for Italy. Between and within event residuals were analyzed in detail to identify the best models, that is, the ones associated with the best misfit and most limited residual trends with intensity and distance. This analysis led us to select four sets of models for which no significant trend in the between- and within-event residuals is detected. These models are considered to be valid over a wide range of Mw covering?~?3.5–7.0.     

An overview of joint inversion in earthquake source imaging

We reviewed joint inversion studies of the rupture processes of significant earthquakes, using the definition of a joint inversion in earthquake source imaging as a source inversion of multiple kinds of datasets (waveform, geodetic, or tsunami). Yoshida and Koketsu (Geophys J Int 103:355–362, 1990), and Wald and Heaton (Bull Seismol Soc Am 84:668–691, 1994) independently initiated joint inversion methods, finding that joint inversion provides more reliable rupture process models than single-dataset inversion, leading to an increase of joint inversion studies. A list of these studies was made using the finite-source rupture model database (Mai and Thingbaijam in Seismol Res Lett 85:1348–1357, 2014). Outstanding issues regarding joint inversion were also discussed.     

On the selection of GMPEs for Vrancea subcrustal seismic source

The Vrancea subcrustal seismic source is characterized by large magnitude ( $M_{W} \ge 7$ ) intermediate-depth earthquakes that occur two or three times during a century on average. In this study several procedures are used to grade four candidate ground motion prediction equations proposed for Vrancea source in the SHARE project. In the work of Delavaud et al. (J Seismol 16(3):451–473, 2012) four ground motion prediction models developed for subduction zones (Zhao et al. in Bull Seism Soc Am 96(3):898–913, 2006; Atkinson and Boore in Bull Seism Soc Am 93(4):1703–1729, 2003; Youngs et al. in Seism Res Lett 68(1):58–73, 1997; Lin and Lee in Bull Seism Soc Am 98(1):220–240, 2008) are suggested as suitable for Vrancea subcrustal seismic source. The paper presents the appropriateness analysis of the four suggested ground motion prediction equations done using a dataset of 109 triaxial accelerograms recorded during seven Vrancea seismic events with moment magnitude $M_{W}$ between 5.4 and 7.4, occurred in the past 35 years. The strong ground motions were recorded in Romania, as well as in Bulgaria, Republic of Moldova and Serbia. Based on the ground motion dataset several goodness-of-fit measures are used in order to quantify how well the selected models match with the recorded data. The compatibility of the four ground motion prediction models with respect to magnitude scaling and distance scaling implied by strong ground motion dataset is investigated as well. The analyses show that the Youngs et al. (Seism Res Lett 68(1):58–73, 1997) and Zhao et al. (Bull Seism Soc Am 96(3):898–913, 2006) ground motion prediction models have a better fit with the data and can be candidate models for Probabilistic Seismic Hazard Assessment.     

The French seismic CATalogue (FCAT-17)

In regions that undergo low deformation rates, as is the case for metropolitan France (i.e. the part of France in Europe), the use of historical seismicity, in addition to instrumental data, is necessary when dealing with seismic hazard assessment. This paper presents the strategy adopted to develop a parametric earthquake catalogue using moment magnitude M_w, as the reference magnitude scale to cover both instrumental and historical periods for metropolitan France. Work performed within the framework of the SiHex (SIsmicité de l’HEXagone) (Cara et al. Bull Soc Géol Fr 186:3–19, 2015. doi: 10.2113/qssqfbull.186.1.3) and SIGMA (SeIsmic Ground Motion Assessment; EDF-CEA-AREVA-ENEL) projects, respectively on instrumental and historical earthquakes, have been combined to produce the French seismic CATalogue, version 2017 (FCAT-17). The SiHex catalogue is composed of ~40,000 natural earthquakes, for which the hypocentral location and M_w magnitude are given. In the frame of the SIGMA research program, an integrated study has been realized on historical seismicity from intensity prediction equations (IPE) calibration in M_w detailed in Baumont et al. (submitted) companion paper to their application to earthquakes of the SISFRANCE macroseismic database (BRGM, EDF, IRSN), through a dedicated strategy developed by Traversa et al. (Bull Earthq Eng, 2017. doi: 10.1007/s10518-017-0178-7) companion paper, to compute their M_w magnitude and depth. Macroseismic data and epicentral location and intensity used both in IPE calibration and inversion process, are those of SISFRANCE without any revision. The inversion process allows the main macroseismic field specificities reported by SISFRANCE to be taken into account with an exploration tree approach. It also allows capturing the epistemic uncertainties associated with macroseismic data and to IPEs selection. For events that exhibit a poorly constrained macroseismic field (mainly old, cross border or off-shore earthquakes), joint inversion of M_w and depth is not possible, and depth needs to be fixed to calculate M_w. Regional a priori depths have been defined for this purpose based on analysis of earthquakes with a well constrained macroseismic field where joint inversion of M_w and depth is possible. As a result, 27% of SISFRANCE earthquake seismological parameters have been jointly inverted and for the other 73% M_w has been calculated assuming a priori depths. The FCAT-17 catalogue is composed of the SIGMA historical parametric catalogue (magnitude range between 3.5 up to 7.0), covering from AD463 to 1965, and of the SiHex instrumental one, extending from 1965 to 2009. Historical part of the catalogue results from an automatic inversion of SISFRANCE data. A quality index is estimated for each historical earthquake according to the way the events are processed. All magnitudes are given in M_w which makes this catalogue directly usable as an input for probabilistic or deterministic seismic hazard studies. Uncertainties on magnitudes and depths are provided for historical earthquakes following calculation scheme presented in Traversa et al. (2017). Uncertainties on magnitudes for instrumental events are from Cara et al. (J Seismol 21:551–565, 2017. doi: 10.1007/s10950-016-9617-1).     

Seismic vulnerability scenarios of Unreinforced Masonry churches in New Zealand

A vulnerability analysis of c.300 unreinforced Masonry churches in New Zealand is presented. The analysis uses a recently developed vulnerability index method (Cattari et al. in Proceedings of the New Zealand Society for Earthquake Engineering NZSEE 2015 conference, Rotorua, New Zealand, 2015a; b; SECED 2015 conference: earthquake risk and engineering towards a Resilient World, Cambridge; Goded et al. in Vulnerability analysis of unreinforced masonry churches (EQC 14/660)—final report, 2016; Lagomarsino et al. in Bull Earthq Eng, 2018), specifically designed for New Zealand churches, based on a widely tested approach for European historical buildings. It consists of a macroseismic approach where the seismic hazard is defined by the intensity and correlated to post seismic damage. The many differences in typologies of New Zealand and European churches, with very simple architectural designs and a majority of one nave churches in New Zealand, justified the need to develop a method specifically created for this country. A statistical analysis of the churches damaged during the 2010–2011 Canterbury earthquake sequence was previously carried out to develop the vulnerability index modifiers for New Zealand churches. This new method has been applied to generate seismic scenarios for each church, based on the most likely seismic event for 500 years return period, using the latest version of New Zealand’s National Seismic Hazard Model. Results show that highly vulnerable churches (e.g. stone churches and/or with a weak structural design) tend to produce higher expected damage even if the intensity level is lower than for less vulnerable churches in areas with slightly higher seismicity. The results of this paper provide a preliminary tool to identify buildings requiring in depth structural analyses. This paper is considered as a first step towards a vulnerability analysis of all the historical buildings in the country, in order to preserve New Zealand’s cultural and historical heritage.     

Fourier spectral- and duration models for the generation of response spectra adjustable to different source-, propagation-, and site conditions

One of the major challenges related with the current practice in seismic hazard studies is the adjustment of empirical ground motion prediction equations (GMPEs) to different seismological environments. We believe that the key to accommodating differences in regional seismological attributes of a ground motion model lies in the Fourier spectrum. In the present study, we attempt to explore a new approach for the development of response spectral GMPEs, which is fully consistent with linear system theory when it comes to adjustment issues. This approach consists of developing empirical prediction equations for Fourier spectra and for a particular duration estimate of ground motion which is tuned to optimize the fit between response spectra obtained through the random vibration theory framework and the classical way. The presented analysis for the development of GMPEs is performed on the recently compiled reference database for seismic ground motion in Europe (RESORCE-2012). Although, the main motivation for the presented approach is the adjustability and the use of the corresponding model to generate data driven host-to-target conversions, even as a standalone response spectral model it compares reasonably well with the GMPEs of Ambraseys et al. (Bull Earthq Eng 3:1–53, 2005), Akkar and Bommer (Seismol Res Lett 81(2):195–206, 2010) and Akkar and Cagnan (Bull Seismol Soc Am 100(6):2978–2995, 2010).     

A probabilistic seismic hazard assessment for the Turkish territory—part I: the area source model

The seismic zoning map of Turkey that is used in connection with the national seismic design code (versions issued both in 1997 and 2007) is based on a probabilistic seismic hazard assessment study conducted more than 20 years ago (Gülkan et al. in En son verilere göre haz?rlanan Türkiye deprem bölgeleri haritas?, Report No: METU/EERC 93-1, 1993). In line with the efforts for the update of the seismic design code, the need aroused for an updated seismic hazard map, incorporating recent data and state-of-the-art methodologies and providing ground motion parameters required for the construction of the design spectra stipulated by the new Turkish Earthquake Design Code. Supported by AFAD (Disaster and Emergency Management Authority of Turkey), a project has been conducted for the country scale assessment of the seismic hazard by probabilistic methods. The present paper describes the probabilistic seismic hazard assessment study conducted in connection with this project, incorporating in an area source model, all recently compiled data on seismicity and active faulting, and using a set of recently developed ground motion prediction equations, for both active shallow crustal and subduction regimes, evaluated as adequately representing the ground motion characteristics in the region. The area sources delineated in the model are fully parameterized in terms of maximum magnitude, depth distribution, predominant strike and dip angles and mechanism of possible ruptures. Resulting ground motion distributions are quantified and presented for PGA and 5 % damped spectral accelerations at T = 0.2 and 1.0 s, associated with return periods of 475 and 2475 years. The full set of seismic hazard curves was also made available for the hazard computation sites. The second part of the study, which is based on a fault source and smoothed seismicity model is covered in Demircioglu et al. in Bull Earthq Eng, (2016).     

Probabilistic seismic hazard assessment for the two layer fault system of Antalya (SW Turkey) area

Southwest Turkey, along Mediterranean coast, is prone to large earthquakes resulting from subduction of the African plate under the Eurasian plate and shallow crustal faults. Maximum observed magnitude of subduction earthquakes is Mw = 6.5 whereas that of crustal earthquakes is Mw = 6.6. Crustal earthquakes are sourced from faults which are related with Isparta Angle and Cyprus Arc tectonic structures. The primary goal of this study is to assess seismic hazard for Antalya area (SW Turkey) using a probabilistic approach. A new earthquake catalog for Antalya area, with unified moment magnitude scale, was prepared in the scope of the study. Seismicity of the area has been evaluated by the Gutenberg-Richter recurrence relationship. For hazard computation, CRISIS2007 software was used following the standard Cornell-McGuire methodology. Attenuation model developed by Youngs et al. Seismol Res Lett 68(1):58–73, (1997) was used for deep subduction earthquakes and Chiou and Youngs Earthq Spectra 24(1):173–215, (2008) model was used for shallow crustal earthquakes. A seismic hazard map was developed for peak ground acceleration and for rock ground with a hazard level of a 10% probability of exceedance in 50 years. Results of the study show that peak ground acceleration values on bedrock change between 0.215 and 0.23 g in the center of Antalya.     

Neo-deterministic seismic hazard scenarios for India—a preventive tool for disaster mitigation

Current computational resources and physical knowledge of the seismic wave generation and propagation processes allow for reliable numerical and analytical models of waveform generation and propagation. From the simulation of ground motion, it is easy to extract the desired earthquake hazard parameters. Accordingly, a scenario-based approach to seismic hazard assessment has been developed, namely the neo-deterministic seismic hazard assessment (NDSHA), which allows for a wide range of possible seismic sources to be used in the definition of reliable scenarios by means of realistic waveforms modelling. Such reliable and comprehensive characterization of expected earthquake ground motion is essential to improve building codes, particularly for the protection of critical infrastructures and for land use planning. Parvez et al. (Geophys J Int 155:489–508, 2003) published the first ever neo-deterministic seismic hazard map of India by computing synthetic seismograms with input data set consisting of structural models, seismogenic zones, focal mechanisms and earthquake catalogues. As described in Panza et al. (Adv Geophys 53:93–165, 2012), the NDSHA methodology evolved with respect to the original formulation used by Parvez et al. (Geophys J Int 155:489–508, 2003): the computer codes were improved to better fit the need of producing realistic ground shaking maps and ground shaking scenarios, at different scale levels, exploiting the most significant pertinent progresses in data acquisition and modelling. Accordingly, the present study supplies a revised NDSHA map for India. The seismic hazard, expressed in terms of maximum displacement (Dmax), maximum velocity (Vmax) and design ground acceleration (DGA), has been extracted from the synthetic signals and mapped on a regular grid over the studied territory.     

Hazard-dependent soil factors for site-specific elastic acceleration response spectra of Italian and European seismic building codes

To define the seismic input in non-liquefiable soils, current seismic standards give the possibility to treat local site effects using a simplified approach. This method is generally based on the introduction of an appropriate number of soil categories with associated soil factors that allow modifying the shape of the elastic acceleration response spectrum computed at rocky (i.e. stiff) sites. Although this approach is highly debated among researchers, it is extensively used in practice due to its easiness. As a matter of fact, for standard projects, this method represents the driving approach for the definition of the seismic input. Nevertheless, recent empirical and numerical studies have risen doubts about the reliability and safety of the simplified approach in view of the tendency of the current soil factors of Italian and European building codes to underestimate the acceleration at the free surface of the soil deposit. On the other hand, for certain soil classes, the current soil factors seem to overestimate ground amplification. Furthermore, the occurrence of soil nonlinearity, whose magnitude is linked to both soil type and level of seismic intensity, highlights the fallacy of using constant soil factors for sites with a different seismic hazard. The objective of this article is to propose a methodology for the definition of hazard-dependent soil factors and simultaneously quantify the reliability of the coefficients specified in the current versions of Eurocode 8 (CEN 2005) and Italian Building Code (NTC8 2008 and revision NTC18 2018). One of the most important outcome of this study is the quantification of the relevance of soil nonlinearity through the definition of empirical relationships between soil factors and peak ground acceleration at outcropping rock sites with flat topological surface (reference condition).     

Numerical modeling of hydrodynamics and sediment transport—an integrated approach

Point measurement-based estimation of bedload transport in the coastal zone is very difficult. The only way to assess the magnitude and direction of bedload transport in larger areas, particularly those characterized by complex bottom topography and hydrodynamics, is to use a holistic approach. This requires modeling of waves, currents, and the critical bed shear stress and bedload transport magnitude, with a due consideration to the realistic bathymetry and distribution of surface sediment types. Such a holistic approach is presented in this paper which describes modeling of bedload transport in the Gulf of Gdańsk. Extreme storm conditions defined based on 138-year NOAA data were assumed. The SWAN model (Booij et al. 1999) was used to define wind–wave fields, whereas wave-induced currents were calculated using the Ko?odko and Gic-Grusza (2015) model, and the magnitude of bedload transport was estimated using the modified Meyer-Peter and Müller (1948) formula. The calculations were performed using a GIS model. The results obtained are innovative. The approach presented appears to be a valuable source of information on bedload transport in the coastal zone.     

Subsurface Hydrology of the Lake Chad Basin from Convection Modelling and Observations

In the Lake Chad basin, the quaternary phreatic aquifer (named hereafter QPA) presents large piezometric anomalies referred to as domes and depressions whose depths are ~15 and ~60 m, respectively. A previous study (Leblanc et al. in Geophys Res Lett, 2003, doi: 10.1029/2003GL018094) noticed that brightness temperatures from METEOSAT infrared images of the Lake Chad basin are correlated with the QPA piezometry. Indeed, at the same latitude, domes are ~4–5 K warmer than the depressions. Leblanc et al. (Geophys Res Lett, 2003, doi: 10.1029/2003GL018094) suggested that such a thermal behaviour results from an evapotranspiration excess above the piezometric depressions, an interpretation implicitly assuming that the QPA is separated from the other aquifers by the clay-rich Pliocene formation. Based on satellite visible images, here we find evidence of giant polygons, an observation that suggests instead a local vertical connectivity between the different aquifers. We developed a numerical water convective model giving an alternative explanation for the development of QPA depressions and domes. Beneath the depressions, a cold descending water convective current sucks down the overlying QPA, while, beneath the dome, a warm ascending current produces overpressure. Such a basin-wide circulation is consistent with the water geochemistry. We further propose that the thermal diurnal and evaporation/condensation cycles specific to the water ascending current explain why domes are warmer. We finally discuss the possible influence of the inferred convective circulation on the transient variations of the QPA reported from observations of piezometric levels and GRACE-based water mass change over the region.     

Performance evaluation of WAVEWATCH III model in the Persian Gulf using different wind resources

The third-generation wave model, WAVEWATCH III, was employed to simulate bulk wave parameters in the Persian Gulf using three different wind sources: ERA-Interim, CCMP, and GFS-Analysis. Different formulations for whitecapping term and the energy transfer from wind to wave were used, namely the Tolman and Chalikov (J Phys Oceanogr 26:497–518, 1996), WAM cycle 4 (BJA and WAM4), and Ardhuin et al. (J Phys Oceanogr 40(9):1917–1941, 2010) (TEST405 and TEST451 parameterizations) source term packages. The obtained results from numerical simulations were compared to altimeter-derived significant wave heights and measured wave parameters at two stations in the northern part of the Persian Gulf through statistical indicators and the Taylor diagram. Comparison of the bulk wave parameters with measured values showed underestimation of wave height using all wind sources. However, the performance of the model was best when GFS-Analysis wind data were used. In general, when wind veering from southeast to northwest occurred, and wind speed was high during the rotation, the model underestimation of wave height was severe. Except for the Tolman and Chalikov (J Phys Oceanogr 26:497–518, 1996) source term package, which severely underestimated the bulk wave parameters during stormy condition, the performances of other formulations were practically similar. However, in terms of statistics, the Ardhuin et al. (J Phys Oceanogr 40(9):1917–1941, 2010) source terms with TEST405 parameterization were the most successful formulation in the Persian Gulf when compared to in situ and altimeter-derived observations.     

Seismic hazard assessment in the megacity of Blida (Algeria) and its surrounding regions using parametric-historic procedure

The region of Blida is characterized by a relatively high seismic activity, pointed especially during the past two centuries. Indeed, it experienced a significant number of destructive earthquakes such as the earthquakes of March 2, 1825 and January 2, 1867, with intensity of X and IX, respectively. This study aims to investigate potential seismic hazard in Blida city and its surrounding regions. For this purpose, a typical seismic catalog was compiled using historical macroseismic events that occurred over a period of a few hundred years, and the recent instrumental seismicity dating back to 1900. The parametric-historic procedure introduced by Kijko and Graham (1998, 1999) was applied to assess seismic hazard in the study region. It is adapted to deal with incomplete catalogs and does not use any subjective delineation of active seismic zones. Because of the lack of recorded strong motion data, three ground prediction models have been considered, as they seem the most adapted to the seismicity of the study region. Results are presented as peak ground acceleration (PGA) seismic hazard maps, showing expected peak accelerations with 10% probability of exceedance in 50-year period. As the most significant result, hot spot regions with high PGA values are mapped. For example, a PGA of 0.44 g has been found in a small geographical area centered on Blida city.     

Water and Food in the Twenty-First Century

In 2000, the World population was 6.2 billion people; it reached 7 billion in 2012 and is expected to reach 9.5 billion (±0.4) in 2050 and 11 billion (±1.5) in 2100, according to the 2012 UN projections (Gerland et al. in Science 346:234–237, 2014). The trend after 2100 is still one of the global demographic growths, but after 2060, Africa is the only continent where the population would still increase. The amount of water consumed annually to produce the food necessary to meet the needs of the populations varies greatly between countries, from about 600 to 2500 m³/year per capita (Zimmer in L’empreinte eau. Les faces cachées d’une ressource vitale. Charles Léopold Meyer, Paris, 2013), depending on their wealth, their food habits, and the percentage of food waste they generate (on average, 30 % of the food produced is wasted). In 2000, the total food production was on the order of 3300 million tons (in cereal equivalents). In 2014, it is estimated that about 0.8 billion inhabitants of the planet suffer from hunger (FAO in World agriculture: towards 2030–2050. FAO, Rome, 2014. http://www.fao.org/docrep/004/Y3557E/y3557e00.HTM) and do not get the nutrition they need to be in good health or, in the case of children, to grow properly (both physically and intellectually). This food deficit was on the order of 40 million tons of cereal equivalents in 2014. The number of inhabitants with a food deficit was about 0.85 billion before the 2008 crisis and was decreasing annually, but it increased abruptly after 2008 up to 1 billion inhabitants and is slowly decreasing now. Assuming a World average water consumption for food of 1300 m³/year per capita in 2000, 1400 m³/year in 2050, and 1500 m³/year in 2100, a volume of water of around 8200 km³/year was needed in 2000, 13,000 km³/year will be needed in 2050, and 16,500 km³/year in 2100 (Marsily in L’eau, un trésor en partage. Dunod, Paris, 2009). Can bioenergy be added to food production? Will that much water be available on Earth, and where will it come from? Is climate change going to modify the answers to these questions? Can severe droughts occur? Can there be conflicts related to a food deficit? Some preliminary answers and scenarios for food production will be given in this paper from a hydrologist’s viewpoint.     

Wave boundary layers in rotating stratified fluid and near-inertial oscillations

Theory of wave boundary layers (WBLs) developed by Reznik (J Mar Res 71: 253–288, 2013, J Fluid Mech 747: 605–634, 2014, J Fluid Mech 833: 512–537, 2017) is extended to a rotating stratified fluid. In this case, the WBLs arise in the field of near-inertial oscillations (NIOs) driven by a tangential wind stress of finite duration. Near-surface Ekman layer is specified in the most general form; tangential stresses are zero at the lower boundary of Ekman layer and viscosity is neglected below the boundary. After the wind ceases, the Ekman pumping at the boundary becomes a linear superposition of inertial oscillations with coefficients dependent on the horizontal coordinates. The solution under the Ekman layer is obtained in the form of expansions in the vertical wave modes. We separate from the solution a part representing NIO and demonstrate development of a WBL near the Ekman layer boundary. With increasing time t, the WBL width decays inversely proportional to \( \sqrt{t} \) and gradients of fields in the WBL grow proportionally to \( \sqrt{t} \); the most part of NIO is concentrated in the WBL. Structure of the WBL depends strongly on its horizontal scale L determined by scale of the wind stress. The shorter the NIO is, the thinner and sharper the WBL is; the short-wave NIO with L smaller than the baroclinic Rossby scale L_R does not penetrate deep into the ocean. On the contrary, for L?≥?L_R, the WBL has a smoother vertical structure; a significant long-wave NIO signal is able to reach the oceanic bottom. An asymptotic theory of the WBL in rotating stratified fluid is suggested.