Seismic Amplification Research Articles

Three-dimensional broadband simulation of near-fault seismic ground motion considering complete source-path-site effect: Modeled by fast multipole indirect boundary element method

Efficient and accurate numerical methods are essential for analyzing seismic wave propagation and amplification in near-fault complex sites. Understanding the complete process of ground motion simulation, including fault rupture, path propagation, and near-surface complex site response, is crucial for studying earthquake damage mechanisms, seismic zoning, and designing large-scale engineering structures. In this study, we propose a fast multipole indirect boundary element method (FMIBEM) to achieve broadband and high-efficiency simulation, enabling a comprehensive analysis of the complete process involving seismic ground motion. The FMIBEM significantly reduces the computational and storage costs associated with 3D near-fault complex site seismic wave scattering problems to O(N). We validate the accuracy of the method by comparing it with the analytical solution. Compared to the conventional indirect boundary element method (IBEM), our proposed method reduces computational time by over 95 % and storage costs by nearly 90 %. FMIBEM greatly enhances the efficiency of the boundary element method for simulating seismic wave scattering in near-fault complex sites. To demonstrate the effectiveness of our approach, we apply the FMIBEM method to two typical 3D near-fault complex site examples of seismic wave scattering. The simulation results successfully capture both the local site amplification effect and the characteristic near-fault seismic features, such as the hanging wall effect, permanent displacement effect, and large velocity pulse.

Numerical investigation of seismic amplification characteristics in loess ridge region of Xiji, northwest China.

The seismic effects on sloped terrain, which are of paramount importance for engineering design and earthquake risk mitigation, have always been a central focus of earthquake engineering research. In this study, generalized geometric models of loess ridges at varying heights were created, and a three-dimensional nonlinear numerical model was established using FLAC3D. Seismic ground motion time histories at different frequencies and actual earthquake ground motion records were input into the model to analyze the peak acceleration amplification effects experienced by the surface of loess ridges when subjected to SV waves. The study's outcomes reveal that seismic amplification on the slopes of loess ridges is characterized by non-linearity with respect to slope height. Instead, it exhibits rhythmic variations, with the rate of change in these rhythms increasing in correspondence with the frequency of seismic motion and the height of the slope. Under low-intensity seismic motion, a linear increase in acceleration amplification is observed at the ridge's crest concerning the height of the loess ridge. However, under high-intensity seismic motion, the relationship between amplification and slope height becomes less significant. Typically, the peak acceleration at the ridge's crest is reported to be 1.5 to 2.5 times that observed at the slope's base. The amplification effect at the ridge's crest is more pronounced in the low-frequency and high-frequency segments when compared to the mid-frequency range. Conversely, significant amplification is observed in the high-frequency range in the lower sections of the slope near the base. It is further noted that the amplification effect at the ridge's crest displays distinct behavior at different frequencies, characterized by narrow frequency bands of maximum amplification, with peak amplification factors exceeding 10 in some cases. These research findings have practical significance and provide valuable references for engineering construction and seismic risk mitigation planning in loess regions.

Topographic seismic effects and avalanche hazard: A case study of Mount Siella (L’Aquila, Central Italy)

In mountainous areas, snow avalanches could be triggered by the shaking produced by earthquakes. The forces induced by the earthquake can cause an irregular increase of shear strength load down the slope, for the presence of complex surface and buried morphologies. Topographic irregularities generate maximum effects of waves amplification linked to wavelengths comparable to the horizontal dimension of the topographic feature. For this reason, the selected time-histories represent an appropriate input for the two-dimensional numerical response analyses when a dynamic phenomenon produce the resonant motion of a whole mountain. This represents an important earthquake-induced hazard in snow-covered mountain areas with high probability of seismic events. Some valleys are located in regions with scare ground motion data and investments on infrastructures are not always accompanied by adequate protection against earthquake-induced avalanches. The paper points out a simple deterministic approach for selecting a set of real accelerograms applied to a real case of Siella Mountain (Central Italy) where a large avalanche destroying a tourist facility of Rigopiano resort on 18 January 2017. The selected time histories were used as input for the two-dimensional numerical model of the subsoil to evaluate the topographic seismic amplification in ridge and compare it with the results of other authors. These methods suggest that morphology-related inertial effects should be considered as an overload action on snow layers when controlling multi-hazard studies and spatial planning.

Social and seismic structural vulnerability in Zihuatanejo, Guerrero, Mexico

The spatial distribution of the social and seismic structural vulnerabilities in Zihuatanejo (ZIH), Guerrero, Mexico, was estimated. Social vulnerability was assessed considering twelve indicators, including parameters such as access to health services, education, housing, employment, and unfavorable family conditions. Seismic structural vulnerability was evaluated characterizing the structural features of local houses, assessing the type and age of construction, and the quality of building materials. Surveyed households were randomly selected from a statistically significant sample. Our findings indicate that in the western and eastern areas of ZIH the population has high and very high social vulnerability. The main factors that condition these levels of social vulnerability are low-income, female-headed families, and households with marginal access to information technology, such as internet and telephone. Although seismic ground amplification in ZIH is relatively low, the regions to the west and southwest of the city are zones where the impact of strong earthquakes to constructions may be greater than in other areas. In particular, the districts of Lázaro Cárdenas, Benito Juárez, Cuauhtémoc, Emiliano Zapata, Las Mesas, Buenos Aires, Lomas del Quebrachal, and Lomas del Riscal would be affected. In general, houses vulnerable to the impact of earthquakes are in regions where the population is socially more vulnerable. More than 50% of the population and 30% of the houses have high and very high level of social and structural vulnerability, respectively. Our results provide information to the local and federal authorities to strengthen their civil protection and mitigation plans.

Failure Probability and Economic Loss Assessment of a High-Rise Frame Structure under Synthetic Multi-Dimensional Long-Period Ground Motions

Multiple research studies and seismic data analyses have shown that multi-directional long-period ground motion affects crucial and intricate large-scale structures like oil storage containers, long-span bridges, and high-rise buildings. Seismic damage data show a 3–55% chance of long-period ground motion. To clarify, the chance of occurrence is 3% in hard soil and 83% in soft soil. Due of the above characteristics, the aseismic engineering field requires a realistic stochastic model that accounts for long-period multi-directional ground motion. A weighted average seismic amplification coefficient selected NGA database multi-directional long-period ground motion recordings for this study. Due to the significant low-frequency component in the long-period ground motion, this research uses empirical mode decomposition (EMD) to efficiently decompose it into a composite structure with high- and low-frequency components. Given the above, further investigation is needed on the evolutionary power spectrum density (EPSD) functions of high- and low-frequency components. Analyzing the recorded data will reveal these functions and their corresponding parameters. Proper orthogonal decomposition (POD) is needed to simulate samples of high- and low-frequency components in different directions. These samples can be combined to illustrate multi-directional long-period ground motion. Representative samples exhibit the seismic characteristics of long-period multi-directional ground motion, as shown by numerical examples. This proves the method’s engineering accuracy and usefulness. Moreover, this study used incremental dynamic analysis (IDA) to apply seismic vulnerability theory. This study investigated whether long-period ground motions in both x and multi-directional directions could enhance the seismic response of a high-rise frame structure. By using this method, a comprehensive seismic economic loss rate curve was created, making economic loss assessment clearer. This study shows that multi-directional impacts should be included when studying seismic events and calculating structure economic damages.

Seismic Microzonation Map of Chiang Mai Basin, Thailand

The seismic site effect which is controlled by local geological conditions is a key parameter of seismic hazards analysis. This paper presents an observational study of microtremor data to investigate the dynamic characteristics of soil in the Chiang Mai basin (Chiang Mai and Lumphun province), Northern Thailand. The Chiang Mai basin was formed on terrace sediments and alluvium sediments. The horizontal vertical spectral ratio (HVSR) analyses of ambient noise data at 101 sites in the basin were analyzed for an average smoothed HVSR curve to estimate the amplification factor and fundamental resonance frequency of each observation point. We also evaluated the shear wave velocity using the HVSR inversion technique based on the diffuse field assumption. Tests undertaken include a comparison of the HVSR of a significant earthquake that was detected at stations in the basin and a nearby bedrock site. The results indicate that the resonance frequency ranges between 0.15 - 0.4 Hz at sites having large thicknesses of soft sediments. The lowest resonance frequencies occur in the center of the basin, whereas higher resonance frequencies were observed in the areas of the shallowest bedrock in the west and east of the basin. It can be inferred that the western margin of the Chiang Mai basin is a steep slope, while the eastern margin of the basin is a low-angle west-dipping basement. The amplification factor ranges between 3 - 5 times, in the middle of the basin. Most of the Chiang Mai basin area is classified as site D soil (stiff soil) relative to alluvium sediments, and a region of class C soil (very dense soil) conforms to the terrace sediments located on the eastern edge of the basin. The soil classification is based on shear wave velocity (Vs30) determined by HVSR inversion. HIGHLIGHTS HVSR analysis and inversion of HVSR from 101 survey points in Chiang Mai basin The Chiang Mai basin area is at high risk from seismic amplification that amplifies a ground motion between 3 - 5 times in the middle of the basin at a dominant frequency range from 0.15 - 0.4 Hz The lowest Vs30 values location is in the middle of the basin classified as site class E (soft soil), while most of the basin area is classified as site D soil (stiff soil) corresponding to alluvium sediments. The class C soil (very dense soil) area conforms to the terrace sediments located on the eastern edge of the basin GRAPHICAL ABSTRACT

Paleoseismic Analysis of the Walanae Fault Zone in South Sulawesi, Indonesia

The most seismogenic fault of South Sulawesi region is Walanae Fault, which has a moderate seismicity history with magnitudes ranging from Mw 4 to Mw 5. The largest earthquake occurred in 1997 with a magnitude of Mw 5.9. After the Donggala-Palu earthquake assailed Sulawesi Island in 2018, the fault in this region were reactivated, including the Walanae Fault system that has pair parallel faults, West Walanae Fault (WWF) and East Walanae Fault (EWF). This fault zone has a 150-km-long and 3-km-wide fault traces, and should have seismicity potential to produce larger earthquakes than the events measured to date. The resulting radiocarbon ages obtained from the dating of organic samples collected on two tranches along with the EWF support that the Walanae Fault zone has a longer earthquake history in the ranges of 4,000 BP (3,050 cal BP and 3,990 cal BP) and 100-300 AD (101 AD pMC and 340 cal BP). The results of age evidence suggest that the Walanae Fault system is an active fault, and must remain of concern as an earthquake source with potential hazards in the region, comprising the West Walanae Fault (WWF) and the East Walanae Fault (EWF). Both faults are separated by a narrow lowland area of Walanae Depression (25 km). The lowland area sandwiched by these two faults harboring a potential seismic amplification that might be generated by thick sediment filled the lowland. Keywords: seismicity, earthquake, radiocarbon dating, Walanae Fault

Effects of Local Soil Profiles on Seismic Site Response Analysis

Local soil conditions play a significant role in the intensity variations of seismic waves during earthquakes. These variations can be either amplified or de-amplified depending on the specific soil conditions. This study aimed to assess the impact of different soil profiles on seismic site responses. The study considered four types of site profiles: sand (Sa), clay (Cl), sand overlying clay (SaCl), and clay overlying sand (ClSa) profiles. To simulate the ground motion, we selected seven sets of strong earthquake records from the European Strong-Motion Database. These records were selected according to Eurocode-8 with a peak ground acceleration (PGA) of 0.24 g, site class A using REXEL computer program. The records were then applied to the bedrock at a depth of 30 meters. Subsequently, a series of 1-D equivalent linear (EQL) response analyses were performed using the STRATA. Amplification factors (AFs) and surface acceleration time histories provided quantitative evaluations for our analysis results. The results demonstrated that site profiles with clay overlying bedrock (SaCl and Cl profiles) exhibited higher seismic amplification and peak ground acceleration in comparison to site profiles with sand overlying bedrock (Sa and ClSa profiles). The maximum median AF is calculated from the SaCl site profile, while the minimum median AF was calculated from the ClSa profile. The relative difference between the maximum and the minimum median AFs was about 33.7%. Based on these results, we can conclude that soft local soils have a pronounced effect on the amplification of seismic waves compared to stiff local soils.

Seismic responses and vibration control of offshore wind turbines considering hydrodynamic effects based on underwater shaking table tests

AbstractThe recent construction of numerous offshore wind turbines (OWTs) in seismically active areas worldwide has stimulated research on seismic evaluation and vibration control design for OWTs. Unlike the onshore counterparts, the hydrodynamic effects on the seismic responses of OWTs need to be studied. Besides, the equipment in the nacelle of an OWT is highly sensitive to acceleration. Significant dynamic amplification on the nacelle under horizontal earthquake excitation can cause the malfunction of power generation and even seriously threaten the safety of OWTs. As a promising solution, tuned mass dampers (TMDs) based on the first mode of OWTs need to be tested by various earthquake excitations. In this paper, the seismic amplification effect, the hydrodynamic effects, and the vibration control by a single TMD are investigated through a series of underwater shaking table tests based on a 1:20 scaled model of a 5 MW OWT. The “no water”, “with water”, and “with water and TMD” tests are evaluated and compared. The accelerations of OWTs can be amplified or reduced by the hydrodynamic effects, depending on the natural frequencies and vibration modes of the OWT and the frequency spectrum of the seismic excitation. The earthquake‐induced hydrodynamic damping ratio and hydrodynamic added mass are carefully measured. For the TMD's effect, the single TMD performs reasonably well in seismic vibration control in most cases. Finally, the interaction between hydrodynamic effects and TMD's effect is discussed, and the hydrodynamic damping effect is suggested to be ignored when designing TMDs for OWTs.

The prediction of seismic amplification effect in three-dimensional sedimentary basins and its application

Numerous studies have shown that the basin amplification effect is influenced by characteristic parameters such as basin geometry and media impedance contrast, but quantitative analysis of the effect for three-dimensional (3D) basins is still rare. In this paper, the basin amplification effect is quantified through an aggravation factor (AGF ), which is defined as the ratio between 3D and 1D acceleration response spectra along the basin surface. Considering the 3D geometry of the actual basin, we investigate the sensitivity of aggravation factors to inclination angles, shape ratios, and impedance contrasts by establishing 78 3D trapezoidal sedimentary basin models with different characteristic parameters. Furthermore, we perform a statistical analysis of the aggravation factors and propose their prediction formulas, which are applied to the Euroseistest basin and the Shidian basin. The above analysis reveals that: (1) The effects of inclination angle and shape ratio on the aggravation factor are concentrated in the edge part and central part of the basin, respectively, while the impedance contrast has less influence on the aggravation factor along the basin surface; (2) From the prediction results for the Euroseistest basin, the aggravation factor of the 3D model is higher than that of the 2D model with a maximum error of 22%, while the distribution pattern of the aggravation factor along the surface is similar; and (3) The predicted results for the Shidian basin show that the basin with a small inclination angle has a larger aggravation factor in the edge part and even exceeds the central part; for example, the highest aggravation factor is 2.155 in the edge part of the basin with an inclination angle of 6°.

Sensitivity Study of Seismic Amplification Effect of Large-Scale Sichuan Basin on Key Parameters During the Great Wenchuan Earthquake

The effect of soil parameters on basin amplification effect has been widely investigated, especially for the small and medium-sized basins under plane wave incidence or point source ruptures. However, the sensitivities of seismic amplification effect of large-scale basins with respect to soil parameters during great earthquakes with tremendous rupture faults have obtained relatively less attention. In this paper, based on the established three-dimensional Sichuan basin model, the effects of four material parameters of the basin sediments, including the shear wave velocity, Poisson’s ratio, and the shear quality factor of the Quaternary sediment, as well as the velocity of the rock above the basin crystalline basement (which will be referred as SVQS, PRQS, QFQS, and VCBR, respectively), on the long-period wave amplification patterns of the Sichuan basin during the great Wenchuan earthquake are investigated by using the spectral element method and parallel computing technique. The results show the following: (1) SVQS has the greatest influence on the basin horizontal component ground motions, while the vertical component is comparably insensitive to it. (2) PRQS demonstrates comparable effects on the horizontal and vertical basin ground motions. With the increase of PRQS, the amplitudes and regions of the strong shakings both become smaller. However, the influence of PRQS is less significant compared with SVQS and VCBR. (3) QFQS mainly affects the relatively high-frequency motions inside the basin, and the low-frequency motions are generally insensitive to it. With the reduction of QFQS, the amplitudes and regions of the basin strong ground motions turn a little smaller, but the distribution features are generally unchanged. (4) Effects of VCBR on the horizontal and vertical component basin ground motions are opposite. With the growth of VCBR, the amplitudes and areas of strong horizontal motions increase consequently, but they decrease for the vertical component.

Pan-Cancer Analysis of Copy-Number Features Identifies Recurrent Signatures and a Homologous Recombination Deficiency Biomarker to Predict Poly (ADP-Ribose) Polymerase Inhibitor Response.

Copy-number (CN) features reveal the molecular state of cancers and may have predictive and prognostic value in the treatment of cancer. We sought to apply published CN analysis methods to a large pan-cancer data set and characterize ubiquitous CN signatures across tumor types, including potential utility for treatment selection. We analyzed the landscape of CN features in 260,333 pan-cancer samples. We examined the association of 10 signatures with genomic alterations and clinical characteristics and trained a machine learning classifier using CN and insertion and deletion features to detect homologous recombination deficiency signature (HRDsig) positivity. Clinical outcomes were assessed using a real-world clinicogenomic database (CGDB) of comprehensive genomic profiling linked to deidentified, electronic health record-derived clinical data. CN signatures were prevalent across cancer types and associated with diverse processes including focal tandem duplications, seismic amplifications, genome-wide loss of heterozygosity (gLOH), and HRD. Our novel HRDsig outperformed gLOH in predicting BRCAness and effectively distinguished biallelic BRCA and homologous recombination-repair wild-type (HRRwt) samples pan-tumor, demonstrating high sensitivity to detect biallelic BRCA in ovarian (93%) and other HRD-associated cancers (80%-87%). Pan-tumor prevalence of HRDsig was 6.4%. HRRwt cases represented a significant fraction of the HRDsig-positive cohort, likely reflecting a population with nongenomic mechanisms of HRD. In ovarian and prostate CGDBs, HRDsig identified more patients than gLOH and had predictive value for poly (ADP-ribose) polymerase inhibitor (PARPi) benefit. Tumor CN profiles are informative, revealing diverse processes active in cancer. We describe the landscape of 10 CN signatures in a large pan-cancer cohort, including two associated with HRD. We trained a machine learning-based HRDsig that robustly identified BRCAness and associated with biallelic BRCA pan-tumor, and was predictive of PARPi benefit in real-world ovarian and prostate data sets.

Preliminary result of dominant frequency and seismic amplification in Penajam Paser Utara and its surrounding regions using the HVSR method

East Kalimantan has been designated as the new capital city of Indonesia, precisely in Penajam Paser Utara and Kutai Kartanegara Regency. According to the historical records of seismic activity, there were several destructive earthquakes in East Kalimantan. Therefore, it is necessary to study the characteristics of the local site to assess the seismic hazard potential in the new capital city area and its surroundings. In this research, the Horizontal to Vertical Spectral Ratio (HVSR) method was applied by utilizing microtremor data from 21 seismometers installed in the research area. The results of the HVSR analysis obtained the dominant frequency (f0) and amplification factor (A0) from the H/V curve. Based on the H/V calculation, the highest f0 is 13.04 Hz and the lowest value is 0.58 Hz. Meanwhile, the highest value for A0 is 6.41, and the lowest value is 1.41. The results of the study show that the research area has a low to medium level of seismic hazard.

Automatic identification of sites prone to topographic seismic amplification effects by the current seismic codes

Current seismic codes provide proxies to estimate seismic amplification effects expected in correspondence of some morphological features. To make possible any empirical validation of these proxies, these features must be univocally identified on the basis of an automatic procedure. To this purpose, based on geomorphological considerations, a GIS-based numerical approach has been developed. The results of a morphometric analysis allowed the correct identification and mapping of the landforms of concern, at a detail corresponding to the resolution of the available digital elevation model (DEM). Some case-studies are provided to show the feasibility of the proposed approach.

Development of recommendations for the implementation of seismic risk mitigation policy in the Russian Federation based on world experience

The current state of practice of seismic risk mitigation policy in the following countries is analyzed: Japan, USA, China, Italy and the Russian Federation. In particular, the paper compares seismic retrofit policies for existing buildings and financing mechanisms for comprehensive seismic risk mitigation in the context of each country's regulatory framework. The analysis of the current seismic risk mitigation policy in the Russian Federation leads to the conclusion that it needs serious modernization and reorganization, including: 1) development of a new generation of standards specifying nonlinear analysis methods and 2) development of effective financing mechanisms for the seismic evaluation and seismic modernization of the existing building stock. 
 The aim of this paper is to identify best practices in seismic retrofitting policy that may be useful for the implementation and adjustment of seismic risk mitigation policies in the Russian Federation at the federal and regional levels. 
 The result of the paper is a set of recommendations based on the most effective seismic risk mitigation policy instruments, grouped according to the key stages of the seismic amplification process:
 – risk assessment of existing buildings;
 – knowledge transfer; 
 – setting targets for the seismic modernization; 
 – implementation of the seismic strengthening policy;
 – policy implementation monitoring.

Seismic amplification effects induced by ancient shallow cavities underneath the urban area of the historical city center of Chieti, Italy

Anthropogenic cavities excavated just beneath the walkable floor (about 1–6 m depth) are present in many ancient urban centres, particularly in Europe and along the Mediterranean basin. The oldest caves are Roman constructions and have been used for different purposes over time (i.e., water storage, secret pathways, shelters against sieges, and wars). For this reason, Seismic Microzonation (SM) studies performed in urban areas must consider the presence of these holes in the subsoil, with their effects predicted through numerical simulations of local seismic response on the surface. In this study, we investigate the seismic effects of ancient anthropogenic cavities in Chieti city centre (Italy) through the cavity amplification factor (CAF). A parametric study was carried out on several different dynamic subsoil models. We define CAF as the ratio between the Acceleration Spectral Intensities on the surface and at the bedrock calculated in the period range of 0.1–0.5 s. The 2-dimensional parametric simulations were performed adopting the soil equivalent linear constitutive law by varying: (1) shear wave velocity values of subsoil, (2) cavity dimensions, (3) cavity depths, (4) cavity lining shear wave velocity values. The CAF plots were calculated on the surface for cavity sizes (width x height) varying from 4 × 5 m to 7 × 9 m. Our study demonstrates that CAF values are relevant only in the period range of 0.1–0.5 s. In particular, results show that: (1) CAF values vary from 1% to 15%; (2) the maximum CAF is felt away from the cavity axis at a distance equal to about 1.5 times the cavity width (L); (3) the maximum difference in CAF values at the surface is equal to 40% within a horizontal distance from the cavity axis ranging from 6 to 14 m. Finally, the case study of the city centre of Chieti (Abruzzo Region) is considered to show how to draw CAF maps for microzonation purposes.

Predicting Models for Local Sedimentary Basin Effect Using a Convolutional Neural Network

Although the numerical models can estimate the significant influence of local site conditions on the seismic propagation characteristics near the surface in many studies, they cannot feasibly predict the seismic ground motion amplification in regular engineering practice or earthquake hazard assessment due to the high computational cost and their complex implementation. In this paper, the scattering problem of trapezoidal sedimentary basins, one of the representatives of local complex sites with a relatively small model size, and simplified by practice in this type of study, was selected as the basin model. A series of standard basin models were built to quantify the relationship between the site condition parameters and the site amplification parameters (the peak ground acceleration and the hazard location). In addition, the factors that influence seismic ground motion amplification, such as the basin shape ratio, the soil depth, the basin edge dip angle, the ratio of shear wave velocity between the bedrock and the soil layer, the damping coefficient, and the fundamental frequency, were selected to investigate the sensitivity. A convolutional neural network (CNN) algorithm based on deep learning replacing traditional recursive algorithms was explored to establish a prediction model of basin amplification characteristics. By the Bayesian optimization method, the structural parameters of the CNN predicting model were selected to improve the accuracy of the prediction model. The results show that the optimized CNN models could predict the amplification characteristics of the basin better than the un-optimized CNN models. Three prediction models were established with the site condition parameters as the input parameters and their output parameters were the maximum amplification value of the peak ground acceleration (PGA), the hazard location, and their combination for each basin. To analyze the CNN’s prediction ability, each CNN model used about 80% of the data from the seismic model repose results for training and the remaining data (20%) for testing. By comparing the CNN prediction results with the FE simulation results, the accuracy and rationality of each prediction model were studied. The results show that, compared to a single numerical model, the CNN prediction results of the site amplification features could be quickly obtained by inputting the relevant parameters. Compared to recursive class models, the established CNN prediction model can directly establish the relationships among multiple input and multiple output parameters. A comparison of the three kinds of CNN models shows that the prediction accuracy of the joint parameter model was slightly lower than that of the two single-output models.

Vs30 and depth to bedrock estimates from integrating HVSR measurements and geology-slope approach in the Oslo area, Norway

In order to estimate well-constrained seismic hazard and risk on local scales, the knowledge of site amplification factors is one of several important requirements. Seismic hazard studies on national or regional scales generally provide the level of earthquake shaking only at bedrock conditions, thereby avoiding the difficulties that are caused through local site effects. Oftentimes, local site conditions are not well understood or even non-existent. In this study we investigate an efficient and non-invasive methodology to derive the local average shear wave velocity in the uppermost 30 m of the ground (Vs30). The Vs30 value is a useful parameter to define soil classes and soil amplification used in seismic hazard assessment and to extend the knowledge of the site to include the depth to basement rock. At the level of the municipality of Oslo, there is currently no map available that describes the Vs30, and as such any seismic risk study is lacking potentially critical information on local site amplification. The new proposed methodology includes the use of existing well databases (with knowledge on minimum basement depth), topographic slope derived from Digital Elevation Models (as a proxy for both depth to basement and Vs30, integrated with geological maps) and near-surface Quaternary geological maps. The Horizontal to Vertical Spectral Ratio (HVSR) method and a statistics-based geological mapping tool (COHIBA) are used to integrate the various sources of data estimates. Finally, we demonstrate our new methodology and workflow with data from three different regions within the Oslo municipality and propose an approach to conduct cost-efficient mapping for seismic site amplification on a general municipality scale.

Bedding slope damage accumulation induced by multiple earthquakes

The 2017 catastrophic Xinmocun landslide was triggered on a bedding slope in the Songpinggou Gully, Maoxian County, China. Previous research primarily focused on the dynamic slope response and deformation characteristics of a single earthquake, and focus on the effect of damage accumulation on slope stability is lacking. The shaking table tests were conducted in this study to understand historical earthquake-induced damage accumulation in bedding slopes. The acceleration amplification coefficient (BPGA) and plastic effect coefficient (PEC) were used to reflect the damage accumulation of bedding slope under the influence of multiple earthquakes. The results revealed that the bedding surface-induced seismic motion amplification contributes to damage constrained on the slope sliding surface. The damage accumulation during multiple earthquakes contributed to slope peak ground acceleration (PGA) amplification increasing and model's natural frequency decreasing in non-linearly form. The shortening of the gap between the driving force frequency and the model's natural frequency had a great impact on the slope damage accumulation. These findings suggest that the accumulation of damage caused by historical earthquake amplification contributes significantly to post-earthquake instability. Future evaluations of slope stability should consider the accumulation and reduced frequency of slope deformation associated with multiple earthquakes.

Seismic Stability Limit Analysis of Unsaturated Soil Slopes Reinforced by Frame Beam Anchor Plates

The frame beam anchor plate (FBAP) reinforced slope has been popularized and applied in some fill slope projects. Nevertheless, the existing design method ignores the influence of earthquake action and the suction effect of unsaturated soils. The stability of unsaturated soil slopes reinforced with FBAPs under an earthquake is analyzed based on the upper bound theorem of limit analysis and pseudo-dynamic method to solve the above problems. The influence of the suction effect on the effective weight and strength of unsaturated soils under one-dimensional steady seepage conditions was considered in the derivation of the energy balance equation. A simplified method based on the volume integral of the rotating body is used to calculate the external work rate. Two possible failure modes of anchorage structures are considered when solving internal energy dissipation. Results show that the influence of suction and seepage conditions on slope stability decreases with the increasing soil pore size distribution parameter n and saturated hydraulic conductivity ks. Also, the stability of the slopes is significantly improved with the increase of total rows of anchor plates. Likewise, the stability of slopes decreases with the increase in the horizontal seismic coefficient kh and amplification coefficient fa.