Vertical Ground Motion Research Articles

Novel Evaluation Method for Site Effect on Earthquake Ground Motion Based on Modified Horizontal to Vertical Spectral Ratio

The effect of local site conditions on the earthquake ground motion is a very important factor to be considered in engineering seismic fortification. Many methods, such as numerical simulation methods based on site analysis models and statistical empirical relation methods based on the earthquake ground motion observations and numerical simulation data, have been used to consider the site effects in actual engineering seismic fortification and earthquake disaster assessment. The statistical analysis to obtain characteristic parameters of site condition effect based on strong motion and microtremor records become an economical and practical method of determining the designed ground motion of engineering sites, especially for large survey areas and engineering sites where it is difficult to carry out a site survey. In this paper, a novel evaluation method for site effect on earthquake ground motion is proposed. The new method is based on the horizontal to vertical spectral ratio (HVSR) method, but the original HVSR is replaced by a modified HVSR considering the effect of the soil layer on the vertical ground motion. In order to build the model and determine the corresponding parameters of the modified HVSR, first, the ground motions in the bedrock below the soil layer are calculated using the one-dimensional equivalent linear method. These calculated records are independent of the influence of the downgoing wavefield, and the differences between the ground surface to bedrock spectral ratio (SBSR). The HVSR for the local sites of ground motion observation stations are analyzed using the strong ground motion records from the Kiban-Kyoshin network (KiK-net) in Japan. The statistical characteristics of the relationship between SBSR and HVSR are revealed, and then, a quantitative relationship between SBSR/HVSR and HVSR is established. The proposed evaluation method for the site effect has the advantage that the original HVSR method only requires ground motion records on the ground surface of the site, and it further considers the influence of the vertical seismic effect on the accuracy of the HVSR method. The proposed method can characterize the influence of the site conditions on ground motion more reasonably than the conventional method.

Seismic performance of a novel three-dimensional isolation bearing

Structural isolation technology has been proven to be an effective means of realizing the seismic resilience of structures. Traditional horizontal isolation bearing can not effectively isolate vertical ground motions, therefore, it is of importance to develop high-performance three-dimensional isolation bearings. This study proposes a novel three-dimensional isolation bearing composed of a horizontal laminated lead rubber bearing (LRB) and a vertical ring spring bearing (RSB) arranged vertically in series. Three specimens were designed and experimentally investigated for the horizontal and vertical mechanical behaviors of the bearing. The three-dimensional vibration control of a six-story structure was analyzed using the proposed isolation bearing. Test results indicate that the proposed three-dimensional isolation bearing has a reliable connecting structure and the design can achieve horizontal and vertical decoupling of the bearing. The horizontal energy dissipation performance of the three-dimensional isolation bearing is stable regardless of the horizontal displacements and compressive stresses, and the bearing inherits the promising horizontal isolation performance of the LRB. The vertical performance of the three-dimensional bearing is mainly attributed to the RSB and inherits the advantages of an RSB with a large bearing capacity and small vertical stiffness. The structure using the three-dimensional isolation bearing has excellent horizontal and vertical isolation performance and can effectively isolate horizontal and vertical ground motions.

Near-fault earthquakes with pulse-like horizontal and vertical seismic ground motion components: Analysis and effects on elastomeric bearings

Near-fault earthquakes have been largely studied in the last years by paying special attention to the occurrence of a pulse-like horizontal seismic ground motion, and to the related effects on structural systems. Conversely, less attention has been paid on the vertical component of the ground motion in such seismic events. Within this framework, the present study is meant at investigating a fairly overlooked special case, that is the occurrence of near-fault earthquakes exhibiting a pulse-like seismic ground motion along the horizontal direction and the vertical one. Specifically, the variational mode decomposition technique is employed to prepare and characterize two subsets of near-fault earthquake records that consist of fault-normal and vertical seismic ground motion components. One subset collects earthquake records with pulse-like waveform in both velocity components, whereas a pulse-like waveform in the fault-normal velocity component only takes place in the earthquake records of the second subset. If both fault-normal and vertical components embed a dominant pulse-like waveform, then it is found that the ratio of the corresponding pulse periods well correlates with the pulse period along the fault-normal direction, while it is uncorrelated with respect to the pulse period along the vertical direction. Next, it is investigated the displacement demand of high-damping rubber bearings for base-isolated buildings under earthquake records characterized by a horizontal impulsive ground motion together with either a pulse-like or a nonpulse-like vertical shaking, provided that the pulse period in the horizontal direction is similar and the peak ground accelerations are individually the same after scaling. Final results shows that the maximum displacement of elastomeric bearings subjected to a pulse-like horizontal ground motion is moderately amplified, on average, when the vertical excitation is also pulse-like.

Parametric investigation on the effect of sloping topography on horizontal and vertical ground motions

This study investigates the effect of slope site conditions on ground motion amplification based on the seismic response analysis of 3D finite element slope models with different soil types and multidirectional seismic loadings. The numerical results indicate that the amplification ability of the lateral infinite extension slope model on the horizontal x- and y-components of input motion is equivalent and slightly less than that of the vertical component. Then, the effects of several site parameters (soil type, slope height, slope angle and peak acceleration of input motion) on topographic amplification of ground motions are discussed. The ability of topographic amplification decreases with increasing soil's shear wave velocity or peak acceleration of input motion. In addition, the amplification ability does not increase monotonously with increasing slope height or slope angle. Finally, the relationships between the evaluation indices and the distance from the slope crest are discussed. The results show that the maximum topographic amplification factor predominantly occurs near the slope crest within x/H = 1.5, and the correction factor defined in the Chinese seismic code could be insufficient for slope sites with low shear wave velocity soils.

Coastal vs volcanic processes: Procida Island as a case of complex morpho-evolutive response

The island of Procida (Gulf of Naples, Italy) is a site of considerable importance from a historical, cultural, and landscape point of view. The island is located along a volcanic active area in the mid-Tyrrhenian and owes its formation to several explosive eruptions started more than 70 ka BP. Presently, the entire perimeter of the island is bordered by cliffs, often articulated in an alternation of headlands and coves, sometimes with shallow sandy beaches at the base (pocket beaches). However, the presence of different orders of submarine terraced surfaces represents a significant clue to coastal response to former sea-level stands.This paper aims at reconstructing the main coastal changes that occurred in the area during the Holocene mainly driven by the interaction between the post-glacial sea-level rise, vertical ground movements (VGMs) of volcano-tectonic origin, and wave action. The coastal sector was investigated using a multi-techniques approach including direct and indirect methods, in order to obtain a detailed geomorphological characterization of the whole study area. In particular, data from direct coastal surveys were integrated with photo-interpretation of areal and satellite photos, morphometric analysis of high-resolution DTMs from Lidar and bathymetric data, interpretation of morpho-acoustic data, archaeological, geomorphological and geological sea-level markers. The geomorphological analysis of this multidisciplinary dataset resulted in the detection of the main morphological elements interpreted as evidence of ancient seascapes. In particular, three orders of paleo-shore platforms were mapped in the underwater sector, allowing the evaluation of as many phases of relative sea-level stand, at −23.2 m, −11.2 m, and − 4.2 m MSL dated at approximately 4.0, 2.0, and 1.0 ka BP. These coastal landforms were interpreted as the main consequence of a seacliff retreat, exacerbated by volcano-tectonic intermittent subsidence that favoured their poly-cyclic formation. However, the integration between the geomorphological and meteo-marine analysis allowed discriminating differentiated cliff backwearing responses between the western and eastern coastal sectors of the island, due to a prevailing occurrence of storms from the south-western sector. The proposed methodological approach focused on a multi-temporal geomorphological analysis applied to a multi-modal dataset, aims to comprehensive reconstruct the coastal response of a volcanic high rocky coast to the complex interaction between endogenous and exogenous forcing factors during the Holocene.

Seismic response of the long-span steel truss arch bridge with the thrust under multidimensional excitation

PurposeUnder different ground motion excitation modes, the spatial coupling effect of seismic response for the arch bridge with thrust, seismic weak parts and the internal force components of the control section of main arch ribs are analyzed.Design/methodology/approachTaking a 490 m deck type railway steel truss arch bridge as the background, the dynamic calculation model of the whole bridge was established by SAP2000 software. The seismic response analyses under one-, two- and three-dimension (1D, 2D and 3D) uniform ground motion excitations were carried out.FindingsFor the steel truss arch bridge composed of multiple arch ribs, any single direction ground motion excitation will cause large axial force in the chord of arch rib. The axial force caused by transverse and vertical ground motion excitation in the chord of arch crown area is 1.4–3.6 times of the corresponding axial force under longitudinal seismic excitation. The in-plane bending moment caused by the lower chord at the vault is 4.2–5.5 times of the corresponding bending moment under the longitudinal seismic excitation. For the bottom chord of arch rib, the arch foot is the weak part of earthquake resistance, but for the upper chord of arch rib, the arch foot, arch crown and the intersection of column and upper chord can all be the potential earthquake-resistant weak parts. The normal stress of the bottom chord of the arch rib under multidimensional excitation is mainly caused by the axial force, but the normal stress of the upper chord of the arch rib is caused by the axial force, in-plane and out of plane bending moment.Originality/valueThe research provides specific suggestions for ground motion excitation mode and also provides reference information for the earthquake-resistant weak part and seismic design of long-span deck type railway steel truss arch bridges.

Effect of Excitation-Applied Manners on Permanent Displacements of Planar Slopes Using Dynamic Sliding Blocks Analysis

The sliding block model is widely used to evaluate the stability of slopes under earthquakes. In this model, the horizontal ground motion is usually applied to the parallel to the slope, whereas the vertical ground motion is commonly ignored. This study investigated the effects of different excitation-applied methods (EAMs) on slope permanent displacements (PDs) using a general sliding block model. For this purpose, three types of ground motion records selected from the NGA-West2 database were applied with six different EAMs to a series of gentle/steep slope sliding systems whose critical accelerations ac ranges from 0.01 to 0.40g. Comparison of the PDs obtained from the two-dimensional (2D) EAM and the other five systems reveal the following: (1) the common practice of applying a one-dimensional (1D) input motion excessively underestimates the PDs of sliding systems, particularly for those with large slope angles and large critical accelerations; and (2) the effects of the vertical component on the arithmetic mean of PDs are ignorable although the impact can reach several times for some cases in which the slopes are located in near-fault areas and affected by pulse-like ground motions. Besides, it is demonstrated in this study that applying the horizontal and vertical base motions simultaneously to the slope can be the most suitable excitation-applied manner for seismic slope stability analysis in the near-fault zone.

Feasibility evaluation of pre-pressed spring devices for vertical isolation of single-layer spherical lattice shell structures

Single-layer spherical lattice shells are typical spatial structures for large-scale landmarks and public buildings. If such buildings are located in strong-earthquake zones, their seismic resilience must be considered. Long-span spatial structures are highly sensitive to multi-component ground motions, and vertical ground shakings lead to strong structural vibrations. Although a few vertical isolators with invariant stiffness have been developed, they are generally too stiff to effectively isolate vertical seismic shakings. In this paper, a nonlinear vertical isolator using pre-pressed and restrained helical springs called pre-pressed spring device (PSD) is proposed. The main advantages of the PSD are that it not only provides a high first stiffness and large bearing force to support the weight of the isolated object but also possesses sufficiently low stiffness to isolate vertical ground motions. In a vertical isolation system, PSDs are employed as basic load-carrying elements, and viscous dampers can be introduced into the system to function as additional energy dissipation devices. The configuration, working principle, and mechanical model of the newly developed PSD are described and explained in detail. Cyclic loading experiments were performed on a prototype PSD to investigate its actual force–displacement relationship. The experimental results showed that the PSD specimen exhibited multilinear elastic behaviors with clear first and isolation stiffness properties. A novel numerical model of the PSD was constructed, and the accuracy of the model was validated by comparing the simulation and experimental results. Subsequently, PSD-damper assemblies and friction pendulum bearings (FPBs) were used to form three-dimensional (3D) isolation bearings for a single-layer spherical lattice shell with surrounding columns. The seismic responses of the controlled structure were evaluated using nonlinear time-history analysis. The numerical results revealed that the PSDs achieved effective static-load support and vertical isolation, and that the entire 3D isolation bearings significantly improved the seismic behavior of the lattice shell structures in all three directions.

Ground Motion Prediction Equations for the Vertical Component from Subduction Interface Earthquakes in Japan Using Site Classes as the Site Term

ABSTRACT A large dataset from earthquakes up to the end of 2012 with a reliable earthquake tectonic category was used to develop a ground motion prediction equation (GMPE) for the vertical strong motions from the subduction interface earthquakes in Japan. Guided by the increase in the maximum log likelihood of the regression model, a minor extension on the maximum usable period was applied so that more records can be used at long spectral periods. A bilinear magnitude scaling function hinged at a moment magnitude (Mw) of 7.1 was adopted, and the scaling rate for events with Mw>7.1 is less than that for the other events. Site period-based site classes were used as the site parameter without a nonlinear site term. We used two datasets with the first dataset including strong-motion records from large events at stations with inferred site classes, and these records were removed in the second dataset so that all sites have a measured shear wave velocity profile down to the engineering bedrock. We found that excluding these records from sites with inferred site classes improved the model fit significantly. We modeled the effect of volcanic zones using the slant distance passing a set of volcanic zones. We also found that the between-site standard deviations for the vertical component in this study were generally less than those for the horizontal component at nearly all spectral periods. The total model standard deviations from this study are generally less than or similar to those from the GMPEs for the vertical ground motions for other earthquake categories. The distributions of between-site residuals with site period or TVS30 (120/VS30 in m/s) are not significantly biased, suggesting that the site term coefficients can be interpolated between that site class terms if a continuous predicted spectrum with site period or TVS30 is required.

GMPEs for elastic input energy spectra of horizontal and vertical offshore ground motions based on the ETMC database in Japan

In this study, the characteristics of offshore ground motions related to elastic relative and absolute input energy are investigated, and ground-motion prediction equations (GMPEs) for elastic input energy of offshore ground motions are proposed. The GMPEs are developed using mixed-effects models calibrated through regression analysis of elastic responses which are derived from dynamic analyses of single-degree-of-freedom (SDOF) systems subjected to offshore ground motions. To compare the differences between offshore and onshore ground motions with regard to input energy, an onshore GMPE is derived from the onshore database. The ground motion database includes 892 offshore records and 4033 onshore records; the offshore and onshore records are collected from the same set of 273 earthquakes. To quantitatively analyze the elastic input energy of offshore ground motions, the moment magnitude, tectonic source type, focal depth, hypocentral distance and site condition are considered in the proposed equations. A comparison and analysis of the relative and absolute input energy of offshore and onshore ground motions manifest that the horizontal input energy spectra of the entire period band and the vertical input energy spectra of moderate and long period band of offshore ground motions are larger than those of onshore motions of all site classes, except that the vertical input energy of offshore motions is slightly smaller than that of onshore motions for short periods due to the combined effects of water layer and soft sediments under seafloor. The differences between the relative and absolute input energy of offshore ground motions and comparisons of the proposed GMPEs with others from the literature are also discussed in this study. The comparisons show that the proposal of the GMPE for elastic input energy of the offshore ground motion is necessary due to the offshore ground motion being considerably different from the onshore motion and the proposed onshore GMPEs. • The prediction equations for elastic input energy of offshore ground motions are proposed, providing the seismic demand for the energy-based seismic design of offshore structures. • The site condition of offshore ground motions is significantly different from those of onshore motions. • The offshore ground motions are larger than those of onshore ones for long period due to the effect of thick soft sediments.

Amplification Behaviour of Compressional Waves in Unconsolidated Sediments

Similar to horizontal earthquake motions, vertical motions are amplified depedent on the local site conditions which can be critical for the safety of certain structures. Production of natural gas in Groningen, the Netherlands, results in reservoir compaction causing low magnitude, shallow earthquakes which are recorded with a borehole seismic network. These recordings form an excellent data set to understand how shallow unconsolidated subsurface geology influences the amplification behaviour of compressional waves (P-waves). First, we present borehole and single-station techniques (amplification factors, empirical transfer functions (ETF) and V/H spectral ratio implementations) to quantify vertical amplification. We show that vertical-wave incidence is a reasonable assumption. All techniques are capable of emphasising the sites with strong amplification of vertical ground motion during an earthquake. Subsequently, we compare ETF with single-station methods with the aim to develop proxies for vertical site-response using spectral ratios. In a second step, we link vertical site-response with shallow subsurface conditions, like the P-wave velocity and peat content. To better understand the amplification mechanisms, we analytically simulate P-wave propagation. In the simulations, we compute synthetic transfer functions using realistic subsurface conditions and make a comparison with the ETF. The simulations support the hypothesis that thin layers of shallow gas, originating from the Holocene peat, result in wave amplification. We observe strong vertical site-response in particular in the eastern part of Groningen, with industrial facilities and pipeline infrastructure in the region. Here, if high vertical amplifications are persistent at large earthquake magnitudes, appreciable levels of vertical loading may be expected. This study demonstrates that vertical motions should be assessed separately from horizontal motions, given that the amplification behaviour of P-waves is affected by distinctive mechanisms.

Multidirectional Linear Site Response Analysis by Applying the SBSR Technique to KiK-net Data

Numerous works have highlighted the importance of the site response analysis of vertical ground motion in the earthquake engineering field. However, most studies have focused on nonlinear site response analysis. Hence, the knowledge of the linear site response analysis of vertical ground motion is inadequate. In this study, we perform multidirectional linear site response analysis by applying the surface-to-borehole spectral ratio (SBSR) technique to the Kiban–Kyoshin strong-motion observation network (KiK-net) seismic data. We find the hyperbolic relationships between multiple natural frequencies and the corresponding fundamental frequency. We propose empirical formulas, which can reduce the error in the multiple natural frequencies estimated by a single-layer model. Moreover, a brief investigation is conducted to provide an extra evidence for a previous correction method to the horizontal-to-vertical spectral ratio (HVSR) technique. The results of this study provide the empirical tools and can be utilized as a reference for the multidirectional linear site response analysis based on seismic observations.

PREDICTION MODEL FOR BASE SHEAR INCREASE DUE TO VERTICAL GROUND MOTION IN FRICTION PENDULUM ISOLATED STRUCTURES

Seismic isolation is one of the most effective seismic hazard mitigation techniques, which has been implemented in many structures. Friction pendulum isolators are one of the most popular isolation devices to achieve energy dissipation and shear resistance that depends on the effective radius and instantaneous vertical force on them. So, the horizontal response of this type of isolators is coupled with the axial load on them, which could change due to vertical acceleration during ground shaking. Thus, it makes consideration of the vertical excitation in the design and analysis phase inevitable, especially for structures in those regions where vertical ground accelerations are more pronounced. In this study a model for the prediction of increase in base shear due to vertical motion for friction pendulum isolated structures is proposed. A simple single friction pendulum isolator system is utilized with the assumption of rigid superstructure on top and subjected to a hundred earthquake ground motions with different characteristics. A multi-layer perceptron model with three layers is utilized, and a simple computer program, which is open-source, is prepared to construct probability curves. With the help of the program, within the range of the considered structural parameters in the study, probability curves related to increase in base shear, maximum isolator displacement and residual isolator displacement can be constructed, and designers can have a rough estimation on modification of these parameters due to vertical ground motion.

A numerical approach for coupled analysis of the seismic response of a cable-moored submerged floating tunnel

A submerged floating tunnel (SFT) is propounded as an efficacious alternative to conventional bridges and underground/submerged tunnels for crossing deep waterways. SFT designers must ensure safe margins and develop approaches to prevail a wide range of plausible situations related to transport, wave, natural vibrations etc. to evaluate the structural stability. To date, only limited researches on this field have been performed to illustrate the significance of seaquake analyses and their effects have been underlined. The present paper intends at numerically simulating a two-dimensional (2D) fluid-structure interaction (FSI) problem in order to scrutinize the dynamic response of an SFT system under bidirectional earthquake actions. Hydrodynamic Pressure due to seismic base excitation is considered as independent nodal variables to represent the gravity influenced inviscid, compressible and irrotational fluid flow effects and the tunnel shell is considered as flexible. This work exposes the importance of the input seismic excitation characteristics that governs the distribution of the induced internal acceleration/force around the lining of the tunnel. Numerical results indicate that the increment rate of the internal acceleration in high SFT caused by vertical ground motion is nearly by 200% when compared to the low-laying tunnel. It is confirmed that long-period record may amplify the overall response of the SFT (up to 80%) when the tunnel approaches the ocean surface, as well as the mooring tensile force to a lesser extent. Finally the proposed coupled numerical procedure suggests that earthquake response spectrum in various intensity levels has an influential role in the response of long-span SFTs and special attention should be paid to the seismic design of such structures.

A seismological phenomenon preceding the 2017 Ms7.0 Jiuzhaigou earthquake

On 8 August 2017, a Ms7.0 earthquake occurred in Jiuzhaigou in the Sichuan Province of China. In this study, we obtained the vertical continuous data recorded at 12 nearby broadband seismometers from April to December 2017, in order to characterize the temporal and spatial variations in the vertical ground motion prior to the onset of the earthquake. Using the self-mutual information method, we determined that from July to August 2017, the self-mutual information value of the vertical ground motion increased at several stations. The spatiotemporal evolution also shows that the region of highest value migrates from south to north toward the earthquake epicenter. Among them, the change of SPA (the station closest to the epicenter) is the most prominent. We believe that this phenomenon is related to the formation of the Jiuzhaigou earthquake. Our work, in combination with other published works, indicates that the Jiuzhaigou earthquake was caused by the continued eastward movement and obstruction of the Qinghai Tibet Plateau by the Sichuan Basin, and the movement of Longmenshan fault is also one of the causes of the earthquake.

Numerical Modeling of Rigid and Flexible Footings Constructed on Natural and Contaminated Soil Strata

In this article, a numerical model has been developed in order to examine the effect of rigid and flexible footings vertically loaded on the behavior of oil-contaminated soil layers by black oil with respect of natural soil strata characteristics. The analyses have included modeling the spread rigid and flexible footings founded on natural soil have been collected from south of Iraq, and contaminated specimens of 10% by weight. The thickness of the contaminated layer (D) has been gradually increased from 1.0 m to 4.0 m from footing base. Three footing width (B), 1.0m, 2.0m and 3.0 m have been simulated in the study. The finite element package PLAXIS 3D has been adopted to simulate the oil contamination problem and to relate the performance of a spread footing supported on natural soil and contaminated soil with different footing width (B) and thickness of contamination layer (D). The outcomes have found out that the vertical ground movement can be reduced by minimum thickness of soil contamination layer. The vertical ground movement has been reduced because of soil contamination when the contamination depth (D) is less than or equal footing width (B) with respect to vertical ground movement of natural soil in case of two types of footing. The behavior of rigid footing has showed more lessening in vertical ground movement as contamination layer thickness (D) 1.0m for all the footing widths.

Infrasound–Electric‐Field Coupling Associated With the 2018 Shinmoe‐Dake Eruptions, Kirishima Volcanic Complex, Japan

Shinmoe-dake volcano, which is within the Kirishima volcanic complex, Japan, erupted from March to June 2018. The eruptions were recorded by various geophysical instruments that were installed 3.1–5.4 km from the crater. Here we present the first documented evidence of infrasound-induced electric-field changes in the near surface at the time of the explosive eruptions. Significant electric-field changes coincide with the infrasound arrivals. An order-of-magnitude estimation of the electric field indicates that the electrokinetic mechanism induced by pore water movement relative to the host rock, is a plausible cause of the observed infrasound–electric-field coupling. The ground displacement and electric-field particle motions suggest that the infrasound waves from the explosive eruptions produce vertical ground motion, and simultaneously induce horizontal groundwater flow, which subsequently generates electric-field changes due to the propagation of the infrasound wave.

On the influence of vertical ground movements on Late-Quaternary sea-level records. A comprehensive assessment along the mid-Tyrrhenian coast of Italy (Mediterranean Sea)

The mid-Tyrrhenian coast is the most complex volcano-tectonic sector in the Mediterranean basin. Here the vertical ground movements (VGMs) due to the interaction between extensive tectonic processes and volcano-tectonic activities have a significant impact on both past and future sea-level evolution. This area represents the youngest basin of the western Mediterranean and it hosts one of the most active volcanic districts, formed by the Campi Flegrei and Vesuvius volcanoes, which are worldwide known for the vertical ground movements accompanying their volcanic activity since the Late Pleistocene. The short-lived alternation of subsidence and uplift has induced great changes in inland areas and abrupt coastal landscape transformations since that time. This study aimed to spatially constrain the magnitude of the vertical displacements which significantly affected this coastal sector during the last millennia. We then reconstructed the multiple relative sea-level oscillations that occurred during the Late-Quaternary by developing a comprehensive WebGIS of sea-level index and limiting points (https://dist.altervista.org/seaproxy/). This includes newly produced sea-level data from recent marine surveys, which were coupled to previously available data standardized according to the recent international guidelines for RSL studies. This allowed producing a multiproxy dataset composed of depositional, erosional, biological, and archaeological sea-level markers, in this very complex Mediterranean area. The collected sea-level data were further compared with a number of geophysical predictions in order to disentangle the different components which influenced the sea-level evolution. Moreover, the tectonic rates derived from the available MIS 5e sea-level data were used to shift the LIG elevations vertically and backwards in time in order to constrain the Last Interglacial RSLs to certain levels depending on the areas. Finally, we used GIS techniques to spatially constrain the coastal sectors more vulnerable to the coupled effects of future sea-level rise and VGMs in the next decades.

Vertical ground-motion prediction equation and the vertical-to-horizontal spectral ratio for crustal earthquakes in Taiwan

We develop a ground motion prediction equation (GMPE) for estimating the vertical ground motion amplitudes for crustal earthquakes in Taiwan. The data set used for the development includes strong-motion recordings mainly from Taiwan earthquakes (M3.5–7.6) and supplemented with large-magnitude earthquakes (M6.5–7.9) from other regions in the Pacific Earthquake Engineering Research Center (PEER) next generation attenuation (NGA)-West2 database. The functional form of the GMPE is similar to that of Phung et al. developed for the horizontal component (P20). The GMPE provides median and standard deviations of peak ground acceleration (PGA) and 5% damped pseudo spectral acceleration response ordinates of the orientation-independent average horizontal component of ground motion (RotD50) for the spectral period of 0.01–10 s. The vertical ground motion developed in this study can be paired with the P20 horizontal component model to estimate a vertical-to-horizontal (V/H) ratio that is unbiased. In the vertical component, we observe significant nonlinear site effects in the period of about 0.2–0.5 s, moderate nonlinear site effects in the period of about 0.01–0.04 s, and small nonlinear site effects in the period of about 0.05–0.075 s. Compared to our horizontal GMPE, anelastic attenuation is faster, VS30-scaling is reduced, and nonlinear site response is weaker for the vertical component.

Performance assessment of composite skirted ground reinforcement system in liquefiable ground under repeated dynamic loading conditions

Occurrence of earthquake generates both horizontal and vertical ground motions. In saturated sands, combination of generated ground motions and pore water pressures induces soil liquefaction. In this study, a composite skirted ground reinforcement system was developed to mitigate generation of pore water pressure in liquefiable soils and also to attenuate incoming ground motions to the foundation. The composite system contains Polyurethane foam as an isolation barrier for ground motion attenuation with stone columns for improving both soil densification and drainage. The performance of this composite reinforcement system was evaluated under repeated acceleration loading conditions to estimate its efficiency. For testing, saturated ground model having 40% and 60% relative density was prepared and investigated with and without the composite reinforcement system. Test results showed that, the developed skirted ground reinforcement system effectively mitigates the interaction of incoming ground motions with the foundation and also improves the reliquefaction resistance of soil compared to that of unreinforced ground.