Preliminary Evaluation of the Impact of Eurocode 8 Draft Revision on the Seismic Zonation of Romania

This study is focused on the impact of the Eurocode 8 draft revision on the seismic zonation of Romania, one of the countries with the highest hazard levels in Europe. In this study, the design response spectra are evaluated for a number of sites in Romania for which both shear wave velocity profiles and ground motion recordings are available. The impact of the proposed changes on the structural design for structures situated in the southern part of Romania is also discussed. The results show considerable differences between the design response spectra computed according to the Eurocode 8 draft revision and the design response spectra from the current Romanian seismic code P100-1/2013. The differences are larger in the case of the sites situated in the southern part of Romania and those which have large design values for the control period TC. In Bucharest, for instance, it was found that the maximum design spectral accelerations would correspond to those from the 2006 version of the code while the maximum design spectral displacements would be significantly smaller than the levels produced by the 1981 or 1992 versions of the code. The results presented herein show that the differences in the seismic hazard and design ground motions are mainly due to the effects of local soil and site conditions and the associated site amplification proposed in the current Romanian seismic code and EC8 draft revision. Moreover, it has been shown that more analyses are needed to apply the seismic actions proposed in Eurocode 8 revision specifically for the sites in Romania under the influence of Vrancea intermediate-depth earthquakes so as to ensure an increased level of seismic safety for structures designed and built in the future.

Site Amplification during Strong Earthquakes Investigated by Vertical Array Records

A number of vertical array records during eight destructive earthquakes in Japan are utilized, after discussing criteria for desirable requirements of vertical arrays, to formulate seismic amplification between ground surface and outcrop base for seismic zonation. A correlation between peak spectrum amplification and Vs (S-wave velocity) ratio (base Vs/surface Vs) was found to clearly improve by using Vs in an equivalent surface layer wherein predominant frequency or first peak is exerted, though the currently used average Vs in top 30 m is also meaningful, correlating positively with the amplification. We also found that soil nonlinearity during strong earthquakes has only a marginal effect even in soft soil sites on the amplification between surface and outcrop base except for ultimate soil liquefaction failure, while strong nonlinearity clearly appears in the vertical array amplification between surface and downhole base. Its theoretical basis has been explained by a simple study on a two-layered system in terms of radiation damping and strain-dependent equivalent nonlinearity.

Living with Earthquakes: Educating masses through earthquake awareness: North East (NE) India perspective

Earthquake is one of the most frightening and destructive phenomena of nature. The northeast India region, as well as its adjoining South-Asian neighbours including Myanmar and Bangladesh, is tectonically and seismically most active. The region categorized under the highest level of seismic hazard potential: Zone V, of the seismic zonation map of India, has experienced nearly 22 large (M ≥7.0) and two great earthquakes (M S ∼ 8.7) in the past 130 years. All these earthquakes caused wide-spread damage over the region. In the recent past, with rapid urbanization combined with a significant population rise as compared to those times when these great/large earthquakes occurred, the seismic vulnerability index has increased manifold. The situation demands widespread dissemination of seismic hazard and preparedness information via community engagement and highlighting on potentially tragic consequences of earthquakes by conducting extensive mock drill exercises & earthquake awareness programmes. In this paper, the role and efforts of the statuary bodies in the region, such as National Disaster Management Authority (NDMA) and CSIR – Northeast Institute of Science and Technology (NEIST) and societal program of Academy of Scientific and Innovative research, to mitigate and minimize seismic hazard by extensive dissemination of earthquake information, via scientific scenario and impact assessment, is holistically compiled.

Terrain Proxy-Based Site Classification for Seismic Zonation in North Korea within a Geospatial Data-Driven Workflow

Numerous seismic activities occur in North Korea. However, it is difficult to perform seismic hazard assessment and obtain zonal data in the Korean Peninsula, including North Korea, when applying parametric or nonparametric methods. Remote sensing can be implemented for soil characterization or spatial zonation studies on irregular, surficial, and subsurface systems of inaccessible areas. Herein, a data-driven workflow for extracting the principal features using a digital terrain model (DTM) is proposed. In addition, geospatial grid information containing terrain features and the average shear wave velocity in the top 30 m of the subsurface (VS30) are employed using geostatistical interpolation methods; machine learning (ML)-based regression models were optimized and VS30-based seismic zonation in the test areas in North Korea were forecasted. The interrelationships between VS30 and terrain proxy (elevation, slope, and landform class) in the training area in South Korea were verified to define the input layer in regression models. The landform class represents a new proxy of VS30 and was subgrouped according to the correlation with grid-based VS30. The geospatial grid information was generated via the optimum geostatistical interpolation method (i.e., sequential Gaussian simulation (SGS)). The best-fitting model among four ML methods was determined by evaluating cost function-based prediction performance, performing uncertainty analysis for the empirical correlations of VS30, and studying spatial correspondence with the borehole-based VS30 map. Subsequently, the best-fitting regression models were designed by training the geospatial grid in South Korea. Then, DTM and its terrain features were constructed along with VS30 maps for three major cities (Pyongyang, Kaesong, and Nampo) in North Korea. A similar distribution of the VS30 grid obtained using SGS was shown in the multilayer perceptron-based VS30 map.

GIS-Based Optimum Geospatial Characterization for Seismic Site Effect Assessment in an Inland Urban Area, South Korea

Soil and rock characteristics are primarily affected by geological, geotechnical, and terrain variation with spatial uncertainty. Earthquake-induced hazards are also strongly influenced by site-specific seismic site effects associated with subsurface strata and soil stiffness. For reliable mapping of soil and seismic zonation, qualification and normalization of spatial uncertainties is required; this can be achieved by interactive refinement of a geospatial database with remote sensing-based and geotechnical information. In this study, geotechnical spatial information and zonation were developed while verifying database integrity, spatial clustering, optimization of geospatial interpolation, and mapping site response characteristics. This framework was applied to Daejeon, South Korea, to consider spatially biased terrain, geological, and geotechnical properties in an inland urban area. For developing the spatially best-matched geometry with remote sensing data at high spatial resolution, the hybrid model blended with two outlier detection methods was proposed and applied for geotechnical datasets. A multiscale grid subdivided by hot spot-based clusters was generated using the optimized geospatial interpolation model. A principal component analysis-based unified zonation map identified vulnerable districts in the central old downtown area based on the integration of the optimized geoprocessing framework. Performance of the geospatial mapping and seismic zonation was discussed with digital elevation model, geological map.

Factors controlling building damage distribution of the November 26 Mw 6.4 Albania earthquake

<p>On November 26, 2019, an earthquake struck the central western part of Albania. It was assessed as Mw 6.4. Its epicenter was located offshore northwestern Durrës, in a distance of about 7 km north of the city and 30 km west from the capital city of Tirana. Its focal depth was about 10 km. Based on the focal plane solutions provided by several seismological institutes and observations, the mainshock was generated by the activation of a NW-SE striking reverse fault. Unfortunately, the earthquake claimed the lives of 52 people. Few hours after the mainshock, the authors visited the earthquake affected areas in order to conduct a field macroseismic survey and geological reconnaissance for assessing the earthquake impact on the building stock. The dominant buildings in the affected area are buildings with load bearing solid brick walls and concrete floor slabs, precast concrete panel buildings and buildings with reinforced concrete (R/C) frame and infill and partition walls. The main characteristic in the majority of these structures is the presence of prefabricated concrete floor slabs with width of 0.7-1.0 m and no connections between them. Building damage was distributed along two ellipses, whose major axis is oriented generally NW-SE. The western ellipse of major damage was observed in Durrës city, located within the Periadriatic Depression, and the eastern one in Thumanë, Laç, Fushë-Krujë, Kamëz towns and Tirana city along the eastern margin of the Tirana Depression. This NW-SE orientation coincides with the strike of the seismogenic fault as it is derived from the fault plane solutions. The first building type presents slight non-structural and structural damage in Durrës city. However, buildings of this type in Thumanë suffered very heavy structural damage including partial collapse resulting in many fatalities. The second type did not suffer significant non-structural or structural damage. The majority of the observed R/C multistorey buildings in Durrës suffered damage to the lower three to four storeys, while the above storeys remained intact. Damage is attributed to the soft soils in the earthquake-affected areas, the undesired resonance phenomena in high buildings, the large duration of the earthquake shaking, the shallow water table in coastal and swamp areas, the pre-existing stress of buildings founded on soft soils characterized by differential settlements and possible liquefaction phenomena, the poor construction quality and workmanship of the affected buildings, the interventions made, the ageing of materials due to differential displacements of the foundation soil, the applicable antiseismic regulations of the time, if ever were applied, the lack of maintenance and inadequate repair after previous destructive earthquakes and the impact of the September 21, 2019 Mw 5.6 earthquake on the buildings of the affected area. The damage are considered typical of an earthquake of this magnitude. The effect of the previous September 21, 2019 Mw 5.6 earthquake in the same area should be also taken into account. Based on the seismic zonation map of Albania, it is concluded that the resulted intensities from the 2019 earthquake are within the limits specified in the Seismic Zonation Map.</p>