Intensity VII Research Articles

Rapid evaluation of earthquake-induced landslides by PGA and Arias intensity model: insights from the Luding Ms6.8 earthquake, Tibetan Plateau

On September 5, 2022, a magnitude 6.8 earthquake occurred along the Xianshuihe Fault Zone in Luding County, Tibetan Plateau, China, leading to a significant outbreak of landslides. The urgent need for a swift and accurate evaluation of earthquake-induced landslides distribution in the affected area prompted this study. This research delves into regional geological data, scrutinizes post-earthquake Peak Ground Acceleration (PGA) and Arias Intensity (Ia) associated with the Luding earthquake, and conducts earthquake-induced landslides risk assessments within the Luding earthquake zone using the Newmark model. Validation of the earthquake-induced landslides risk assessment outcomes rooted in PGA and Ia relies on an earthquake-induced landslides database, revealing Area Under the Curve (AUC) values of 0.73 and 0.84 in respective ROC (Receiver Operating Characteristic) curves. These results unequivocally affirm the exceptional accuracy of earthquake-induced landslides evaluation using Ia calculations, emphasizing its suitability for the swift prediction and evaluation of earthquake-induced landslides. The earthquake-induced landslides risk assessment based on Ia computation reveals the area with extremely high-risk and high-risk of earthquake-induced landslides encompass 0.71% of the entire study area. Notably, these areas are predominantly clustered within seismic intensity VII zones and primarily trace the Moxi fault zone, extending from the southern portion of the middle east along the Dadu River and the Moxi fault, with reach up to Dewei Township in the north and Caoke Township in the south. Hazard-prone regions predominantly align with slopes featuring gradients of 30°–45° and bear a strong correlation with fault activity. Furthermore, the results of this evaluation are harmonious with the findings from remote sensing interpretation and on-site field investigations pertaining to the earthquake-induced landslides. This body of knowledge can serve as a crucial reference for expedited assessment, emergency response and subsequent supplementation of earthquake-induced landslide databases when confronting similar earthquake-induced landslide scenarios.

Catalogue-based spatio-temporal analysis and evaluation of seismic scenarios in the Talysh zone (Azerbaijan)

In this paper, we simulate ground motion shaking of the Talysh zone based on the hybrid stochastic-deterministic approach using catalogue-based spatiotemporal analysis for 1970—2019 from the various local and international sources and the fault source pattern. Data for a homogenous and reliable catalogue are obtained from the International Seismological Center (ISC), European Mediterranean Seismological Center, National Earthquake Information Center, and Republican Center of Seismological Survey at the Azerbaijan National Academy of Science. To evaluate the ground shaking and to characterize its spatial variability, an intensity map was plotted depending on the selected seven active faults and lineaments tracing in the Talysh zone, considering the location, size and length of faults, using empirical relations between magnitude and intensity. The mapping results are presented in terms of intensity distribution. The plotted map shows that shakings with an intensity of VII are observed mainly in the central and western parts of the zone and are predicted to be the highest in the study area. The ground shaking with an intensity VI covers most of the Talysh zone. The magnitude computation results show that a maximum earthquake with Mw=6.2 can be generated by the West Caspian fault.
 This study applied various seismic input parameters and different approaches to give the basic information to evaluate the range of intensity distribution in seismic scenarios. The results will contribute to implementing more solid analyses for advancing earthquake countermeasure plans and seismic hazard analysis.

Blast resistance of ultra high performance concrete-filled steel tube (UHPC-FST) pier against vehicular bombs

Bridge piers will lose axial bearing capacities under accidental or deliberate explosions, which may cause partial or even multi-span collapse of the bridges. Compared with the conventional RC pier, the ultra high performance concrete-filled steel tube (UHPC-FST) pier exhibits superior strength, ductility, and durability, thus having promising applications in the field of blast-resistant bridges. This study aims to experimentally and numerically examine the blast-resistant performance of the UHPC-FST pier under the near-range explosion of Vehicle-Borne Improvised Explosive Devices (VBIED). Firstly, a prototype UHPC-FST pier with earthquake intensity VII was designed following the Chinese specifications, and four 1/4-scale UHPC-FST specimens were scaled and fabricated accordingly. The near-range explosion and succeeding axial compression test were carried out on the specimens with TNT masses of 3 kg, 4 kg, 7 kg, and 10 kg, respectively. Then, full parameters of the Karagozian & Case (K&C) concrete material model applicable to UHPC were systematically calibrated based on the available test data, and the refined finite element (FE) models were established correspondingly based on the explosion and axial compression test. The verification of FE modeling approach was verified by comparing the failure modes and axial force–displacement curves of specimens obtained from the numerical simulation with the test. Finally, two types of VBIED (compact sedan and cargo van) and three standoff distances were selected from the report FEMA-428 and Chinese specifications, and six explosion scenarios were designed correspondingly. The shock wave propagation, shock wave-pier interaction, and the damage evolutions of prototype piers were numerically reproduced. The blast-resistant performance of the prototype UHPC-FST pier was assessed from the aspect of the failure modes and residual axial bearing capacities, which were quantitatively compared with those of conventional RC pier with identical earthquake intensity.

Seismic catastrophes in historical times in Arabia – Destruction of the city of Qalhat (Oman) in the 16th century

The Arabian Peninsula is surrounded by seismically highly active plate margins, while the interior seems to be free from destructive earthquakes. We report two historical earthquakes in Qalhat, Oman, >300 km from any plate boundary and provide archaeoseismological analysis of ruined buildings. The first quake hit the city in 1497 AD with an intensity VII at most; the community survived and damage was repaired. The second event caused total devastation (intensity X-XI), sometime between 1580 and 1592. The city never recovered from the latter; it has been a field of ruins ever since. ShakeMap modeling yielded magnitude Mw 5.5 for the first and Mw 6.5–7.0 for the second earthquake. We suggest that the strike-slip Tiwi Fault or the reverse Qalhat Fault caused the first, while the reverse Qalhat Fault might have caused the second earthquake.

Memory of the Earth and Human Memory of Natural Disasters: the 1953 Earthquake in Western Aragón (Spain)

Occurred in 1953 in Used (Zaragoza province), an earthquake of magnitude 4.7 and intensity VII was the last destructive earthquake in the Aragón region, Spain. The remaining social memory of that event (a type of intangible geological heritage) and its influence on the perception of seismic hazard in the area are explored by means of interviews and a population survey. The results indicate that the memory is lively amongst the population within the epicentral area, both in the generation that experienced it and, to a lesser extent, in the following generations. However, this does not translate into a significant perception of seismic hazard, the latter being more influenced by cultural factors: in the epicentral area it is greater amongst people who did not live through the earthquake, but who have heard familiar stories or have had external information highlighteing its importance. The study of social perception is part of a citizen science project, in which the social memory enters into dialogue with the Memory of the Earth, i.e. the record left by that and other previous earthquakes in geology and landscape. The research on the effects of the shake on people, buildings, and environment has benefited from numerous testimonies from the elderly. Reciprocally, such knowledge is scientifically processed and returned to the citizens in the form of scientific outreach products (book, documentary film, talks), with the aim of promoting scientific culture about natural disasters.

The damaging character of shallow 20th century earthquakes in the Hainaut coal area (Belgium)

Abstract. The present study analyses the impact and damage of shallow seismic activity that occurred from the end of the 19th century until the late 20th century in the coal area of the Hainaut province in Belgium. This seismicity is the second-largest source of seismic hazard in north-western Europe after the Lower Rhine Embayment. During this period, five earthquakes with moment magnitudes (Mw) around 4.0 locally caused moderate damage to buildings corresponding to maximum intensity VII on the European Macroseismic Scale 1998 (EMS-98). Reviewing intensity data from the official macroseismic surveys held by the Royal Observatory of Belgium (ROB), press reports and contemporary scientific studies resulted in a comprehensive macroseismic intensity dataset. Using this dataset, we created macroseismic maps for 28 earthquakes, established a new Hainaut intensity attenuation model and a relationship linking magnitude, epicentral intensity and focal depth. Using these relationships, we estimated the location and magnitude of pre-1985 earthquakes that occurred prior to deployment of the modern digital Belgian seismic network. This resulted in a new updated earthquake catalogue for the Hainaut area for the 1887–1985 period, including 124 events. A comparison with other areas worldwide where currently similar shallow earthquake activity occurs suggests that intensity attenuation is strong in Hainaut. This high attenuation and our analysis of the cumulative effect of the Hainaut seismicity indicate that current hazard maps overestimate ground motions in the Hainaut area. This reveals the need to use more appropriate ground motion models in hazard issues. Another strong implication for earthquake hazard comes from the reliability of the computed focal depths that helps clarifying the hypotheses about the origin of this seismicity. Some events were very shallow and occurred near the surface up to a depth not exceeding 1 km, suggesting a close link to mining activities. Many events, including the largest shallow events in the coal area before 1970, occurred at depths greater than 2 km, which would exclude a direct relationship with mining, but still might imply a triggering causality. A similar causality can also be questioned for other events that occurred just outside of the coal area since the end of the mining works.

SEISMICITY of the NORTHERN CAUCASUS in 2015

Seismic monitoring in the region in 2015 was carried out by a seismic network consisting of 59 stations. Digital equipment was installed at all stations in the second half of the year. The network capability was assessed by the level of seismic noise at the stations: in most of the region, the network provided registration of an earthquake from КR7.0, in the central (including the Greater Sochi region) and eastern parts of the region – КR6.0, and in some local zones with КR5.5. 2,276 earthquakes were registered, 17 earthquakes were felt in the settlements of the Caucasus. The maximum intensity VII at MSK-64 (SSI-17) scale was noted from the earthquake in the territory of Azerbaijan. The earthquake on November 3, which occurred on the platform territory within the Stavropol arch, felt IV at MSK-64. The strongest earthquakes were recorded in the Terek-Caspian and Kura troughs and in the eastern part of the Greater Caucasus. The seismicity of the North Caucasus in 2015 in accordance with the seismicity scale "SOUS-09" was set as the "background average" for the observation period from 1962 to 2015.

Analysis on the Influence of Increasing Seismic Fortification Intensity on Seismic Performance of Underground Station

China Earthquake Parameter Zoning (2016) has increased the seismic fortification intensity in Chengdu from VII to VIII. It is necessary to conduct in-depth discussion on the impact of the seismic performance of the built underground station structure. In this paper, a stratum-structure finite element model is established with a Chengdu subway station as an example. The model boundary adopts viscoelastic boundary, and the ground motion is input in the form of equivalent nodal force. The equivalent linearization method is used to consider the nonlinearity of soil materials. The time-history analysis of seismic fortification intensity of VII and VIII degrees is carried out, respectively. By comparing the calculation results of the two seismic fortification intensity ground motion conditions, it is concluded that the connection between the side wall and the floor is the weakest position of the station structure under the action of the earthquake; the seismic fortification intensity is increased from VII to VIII to the internal force of the structure. It has a relatively large impact, especially the most obvious impact on the bending moment. The results of the verification of the seismic time-history analysis show that the increase of fortification intensity will have a more obvious impact on the structural deformation, and the structural design of the station can meet the safety performance requirements of VII and VIII degrees of seismic fortification. The research has certain reference significance for the seismic safety evaluation of the built underground station structure in Chengdu area.

Seismic site characterization and site response study of Nirsa (India)

The Nirsa block, a coal mining area, and an industrial town lies in the southern part of Dhanbad district, at the border between the Indian states of Jharkhand and West Bengal. This area manifests the significant seismic risk posed by earthquakes, natural as well as induced, of high enough seismic intensity VI and VII from regional and local earthquakes. Hence, it is indispensable to seismically characterize the top surficial layers to reduce the risk associated with earthquakes in this region. We characterize these layers, using ambient noise acquired from multichannel simulation with one receiver and single station method to subsequently invert for shear wave velocities, via iterative global search technique of the guided Monte Carlo method by fitting fundamental mode Rayleigh wave phase velocity dispersion curves and horizontal-to-vertical spectral ratios (HVSR). We survey the area to record a sufficient amount of ambient noise within the frequency range of 1–30 Hz at seventy-eight observation points, with uniform spacing of 250 m, covering a total area of about 4 km2. Our results reveal that the bedrock depth lies in the range of 19.5–2.7 m; while Vs30 values vary in the range of 250–950 m/s in the Nirsa region. The variations in fundamental resonance frequencies, obtained from HVSR curves, are found to be more scattered in the range between 2 and 23 Hz. The maps of fundamental resonance frequency, peak HVSRs’ amplitude, bedrock depth and Vs30 derived from this research exhibit good correlation with each other. The Vs30 prediction equation based on the fundamental resonance frequency (fr) and HVSR amplitude (A0) will help future studies to determine Vs30 of unknown regional sites. The efficacy of our results is reliable as there is good concurrence between shear wave velocity profiles, HVSR profiles and litholog data sets. Our results may prove to be important assets to agencies such as National Disaster Management Authorities and Geological Survey of India for construction of seismic microzonation maps in Nirsa.

Application of Statistical Prediction Model to the Reservoir Induced Seismic Risk Analysis of Aqing Hydropower Station in Xizang

Based on field seismic geological survey and previous research results, this paper analyzed tectonic background, seismicity and hydrogeological conditions of Aqing hydropower station in Xizang respectively, then calculated the probability of reservoir induced seismicity. The results showed that it is possible for the reservoir induced seismicity occurring, whose probability is 0.455. In detail, the probabilities of occurring moderate-strong, weak, and micro earthquake are 0.089, 0.070, and 0.296 respectively. Under these circumstances and based on the intensity attenuation relationship of reservoir induced seismicity, it can be deduced that the moderate-strong earthquake would occur with epicentral intensity VII, and the lengths of major axis and minor axis are 6.5 km and 3.3 km respectively.

Fracture Mechanism of Unstable Rock With Double-Crack Control Discontinuity Subjected to High Earthquake Intensities

Unstable rock in the limestone area has typical characteristics of quasimasonry structure and control discontinuity, where the failure essence is the fracture propagation under loads. The unstable rock control discontinuity in the limestone zone was analyzed, and the geological model for a doublecrack unstable rock mass was obtained according to the theory of geomorphologic evolution. The mechanical model and fracture mechanical model for the complex control discontinuity were constructed. Based on the rock weight, the fissure water pressure and the earthquake load, the formula of the fracture stability coefficient was obtained under the maximum circumferential stress criterion. The fracture stability coefficient expression for the unstable rock is rational according to the verifying case analysis. The fracture stability coefficient corresponding to each intensity decreases with the crack length ratio. Under earthquake intensities Ⅷ and Ⅸ, the unstable rock will collapse; the stability of the unstable rock is liable to the coupling effects of the crack length ratio of the main control discontinuity and the earthquake intensity. The critical crack length ratio decreases with the earthquake intensity. Under earthquake intensity Ⅶ, the theoretical value of the critical crack length ratio is 25.8%, which is slightly less than the actual value of 27.7%, and on the slightly safer side. The fracture stability coefficient expression has good applicability. The research results provide an important theoretical support for the treatment of such unstable rock masses.

ANALYSIS OF A PEAK GROUND ACCELERATION VALUE AND EARTHQUAKE INTENSITY USING DONOVAN METHOD IN BANTEN PROVINCE

Analysis of a peak ground acceleration value and earthquake intensity in Banten Province has been carried out using historical earthquake data from 2008 to 2018. This research aims to describe a prone area of the earthquake. The specification of data was a magnitude > 5 SR and the depth 0-70 km. The Donovan method was used to analyze peak ground acceleration value and the earthquake’s intensity. According to the data obtained, 31 earthquake points with a maximum earthquake strength occurred on October 16, 2019, with a depth of 10 km and a magnitude of 6.48 SR. This earthquake was located in Ujung Kulon with coordinates -6.81 LS and 105.113 BT. Based on data analysis result was obtained a peak ground acceleration value and the intensity of earthquake maximum in The Pandeglang Regency with a peak ground acceleration value was 211.56 cm/s2, and intensity of scale VIII and a large risk level of three. While a peak ground acceleration minimum is located in the South Tangerang City was 62.82 cm/s2 with a scale of intensity VII and a moderate risk level.

Seismic damage to ancient monuments in Chiang Saen (Northern Thailand): implication for historical earthquakes in Golden Triangle area

Over the last few decades, three moderate earthquakes (Mw greater than 6.0) occurred in and around the Golden Triangle area (including Myanmar, Thailand and Lao PDR) causing unprecedented damage and loss of lives in the epicentral region. In addition to the damage to modern structures, most heritage structures in Chiang Saen, a major city of the Lan Na kingdom (from the thirteenth to the eighteenth century), were also affected. This work is intended to present observed historical structure damage from recent earthquakes, which could provide evidence for the severity of historical earthquakes from the thirteenth to the eighteenth century. Based on historical records, geological evidence and observed damage to ancient monuments in this historic town, existing heritage stupas and temples constructed since the fourteenth century sustained only minor to moderate damage from these historical earthquakes. Considering the seismic vulnerability of these historical monuments, Chiang Saen might have never been subjected to severe ground shaking greater than MMI intensity VII, similar to the major earthquake in 460 A.D. along the Mae Chan fault, which was responsible for the large-scale liquefaction and inundation of ancient Yonok town. This information could be important for paleoseismological and historical earthquake research to constrain the recurrence interval of major active faults in this area. This article is part of the theme issue 'Environmental loading of heritage structures'.

Seismic response in large-aperture, fully-steerable antenna structure

The aseismic properties of an initial 65-m radio telescope structure in Shanghai with fortification intensity of VII are analyzed under “frequent” and “rare” earthquake conditions via time-history method. Mechanical responsive targets which are crucial to the structure during an earthquake are given in static unitized load mode. Structural weakness (e.g., plastic deformation in certain bars) is observed during the frequent-type earthquake under static unitized load mode. During a rare-type earthquake, artificial ground motion produces the most severe impact on the structure. Regardless of pitching angle model, the antenna structure does not break down during any rare earthquake. After some modifications to the initial design and using the most disadvantageous model ( $5^{\circ}$ pitching angle), all targets of all bars meet the necessary specifications for frequent-type earthquake resistance when aseismic fortification intensity is VIII.

Revisión y ampliación del catálogo sísmico del noroeste de la Península Ibérica previo a 1755 y sus implicaciones en la actividad intraplaca

La base de los estudios de peligrosidad sísmica es disponer de catálogos sísmicos lo más completos posible. En regiones intraplaca, caracterizadas por largos periodos de recurrencia entre terremotos, es esencial obtener un catálogo sísmico con un extenso intervalo temporal. El noroeste de la Península Ibérica (Galicia, Asturias, Cantabria, Castilla y Leon y norte de Portugal) se ha considerado tradicionalmente una zona intraplaca sísmicamente estable, ya que se encuentra alejada de los bordes de placa sísmicamente activos. Sin embargo, crisis sísmicas como las Sarria-Triacastela-Becerreá (Lugo) (1995 y 1997; con eventos de magnitud hasta 5.3) ponen de manisfiesto en esta región un potencial sismogénico de magnitud moderada. En este trabajo se realiza una revisión y ampliación del catálogo sísmico de esta región previo a 1755 (periodo peor documentado del catálogo sísmico), con el objetivo de caracterizar esta sismicidad intraplaca y mejorar la completitud con un nuevo catálogo para el NO peninsular y así poder reconocer si la sismicidad reciente y posterior a 1755 es anómala o si, por el contrario, es característica de esta región. Para ello, se tomó como base el catálogo sísmico oficial español del Instituto Geográfico Nacional (IGN), que es la agencia responsable de la red y alerta sísmica. Se han buscado las fuentes documentales primarias de los terremotos descritos en dicho catálogo, para el margen espacial y temporal considerado, y se han revisado parámetros como la localización, fecha y zonas geográficas afectadas por el terremoto. En este catálogo a los 13 terremotos incluidos por el IGN, se han añadido 10 del catálogo de Ces Fernández (2015) y 4 nuevos, ampliando así el catálogo hasta los 27 terremotos. Tras revisar las fuentes se han modificado: 6 parámetros de fechas, 8 localizaciones y 10 zonas geográficas donde se sintió el sismo. Posteriormente ha sido posible calcular la intensidad de 18 de estos terremotos con dos escalas macrosísmicas (EMS-98 y ESI-07). En este nuevo catálogo las intensidades calculadas se encuentran entre IV y X en EMS-98 y entre VII y XI en la ESI- 07, es decir incluyen eventos de mayor o igual intensidad que los ocurridos después de 1755, que no han sobrepasado la intensidad VI o VII como ocurrió en la crisis de Sarria-Triacastela-Becerreá (Lugo) de 1997. Además, la distribución geográfica de los eventos anteriores a 1755 es similar a los ocurridos posteriormente. Todo ello indicaría que la sismicidad actual y posterior a 1755 no sería una anomalía de la tendencia de la región. En el futuro, para seguir ampliando el catálogo sísmico de esta región, sería necesario integrar estudios multidisciplinares de sismicidad histórica e instrumental y paleosismología, prestando atención a fallas que puedan ser activas, bajo el régimen tectónico actual.

Engineering analysis of strong ground rocking and its effect on tall structures

Two, the most intensive 6-dof ground motion records were selected from a database of a program of acquiring seismic aftershocks at Kefalonia Greek Island as reported by Perron et al. in 2018 [1]. The maximum Modified Mercalli (MM) intensity VII and peak ground velocity 18.4 cm/s reached during these seismic events made it possible to investigate substantial structural response under combined translational and rotational excitations. Respective horizontal-rocking effects are studied first on a simplified cantilever model of a slender tower. Next, the seismic responses of two 10 and 30 story tall buildings and a 160 m, reinforced concrete industrial chimney under the joint rocking and horizontal excitations are investigated in detail. A complicated pattern of translational-rocking seismic effects on slender structures was observed. It was noted that sometimes the presence of seismic rotations about horizontal axis increases the overall response (up to 30%), sometimes it decreases the combined seismic response. The net effect depends primarily on two, the most important structural parameters: fundamental natural period and effective height of the analysed structure. The rocking response spectrum proposed in Eurocode 8 part 6 for slender structures was compared with seismic time history response analyses of the r/c chimney, yielding its substantial conservatism compared with the time history response computations using the chosen records of 6-dof strong ground motion. It is also concluded that the application of the familiar SRSS rule to combine the horizontal and rocking effects may underestimate the overall seismic response. This may be important for future calibrations of the seismic codes including rocking ground motion effects.

Seismic Retrofitting of Concrete Structures

According to the latest seismic zone map of India, about 59 percent of India’s land area is vulnerable to moderate or severe seismic hazard, i.e., prone to shaking of MSK intensity VII and above. In the recent past, most Indian cities have witnessed an excessive rise in multi-storied buildings, super malls, luxury apartments and social infrastructure largely owing to development. The rapid expansion of the built environment in moderate or high-risk cities makes it imperative to incorporate seismic risk reduction strategies in various aspects of urban planning and construction of new structures. During the period 1990 to 2006, India has experienced 6 major earthquakes that have resulted in over 23,000 deaths and caused colossal damage to property, assets, and infrastructure.

A depth-consistent SPT-based empirical equation for evaluating sand liquefaction

Focusing on the deficiencies of the current liquefaction evaluation methods typically on deep sandy-layers of 10m to 20m, a new liquefaction evaluation formula, which is based on the 156 SPT data from liquefaction investigation in China mainland, is proposed. The formula is plausible for wide depth range up to 20m. The formula which takes a hyperbolic function form fits the liquefaction data at shallow depth and predicts satisfactorily deep liquefaction. The liquefaction dataset available from China earthquakes and foreign earthquakes (i.e., Kobe earthquake and ChiChi earthquake) are statistically summarized. The deficiencies of prevailing liquefaction evaluation methods and the CSR method by Seed are pinpointed. To validate the proposed formula, a liquefaction dataset consist of 312 liquefaction data from China mainland and foreign countries is used for re-evaluation. The results indicate that the new formula is quite feasible for wide sandy-layer buried depth, different seismic intensities and varying groundwater tables. Comparing with the current Chinese code methods and the CSR method, the new formula which approaches to an asymptote eliminates the abnormality of the CSR method that decreases inversely when the depth exceeds a certain value. The new formulae solve the deficiency of Chinese codified liquefaction evaluation methods that are conservative for intensity VII at shallow depth <10m, and evenly predict liquefaction superior to the Chinese code methods for intensities VIII and IX at shallow depth. The new formula overcomes the considerably conservative predictions of the code methods on deep soil of 10m to 20m in intensities VIII and IX.

Fault specific GIS based seismic hazard maps for the Attica region, Greece

Traditional seismic hazard assessment methods are based on the historical seismic records for the calculation of an annual probability of exceedance for a particular ground motion level. A new fault-specific seismic hazard assessment method is presented, in order to address problems related to the incompleteness and the inhomogeneity of the historical records and to obtain higher spatial resolution of hazard. This method is applied to the region of Attica, which is the most densely populated area in Greece, as nearly half of the country's population lives in Athens and its surrounding suburbs, in the Greater Athens area. The methodology is based on a database of 24 active faults that could cause damage to Attica in case of seismic rupture. This database provides information about the faults slip rates, lengths and expected magnitudes. The final output of the method is four fault-specific seismic hazard maps, showing the recurrence of expected intensities for each locality. These maps offer a high spatial resolution, as they consider the surface geology. Despite the fact that almost half of the Attica region lies on the lowest seismic risk zone according to the official seismic hazard zonation of Greece, different localities have repeatedly experienced strong ground motions during the last 15kyrs. Moreover, the maximum recurrence for each intensity occurs in different localities across Attica. Highest recurrence for intensity VII (151–156 times over 15kyrs, or up to a 96year return period) is observed in the central part of the Athens basin. The maximum intensity VIII recurrence (115 times over 15kyrs, or up to a 130year return period) is observed in the western part of Attica, while the maximum intensity IX (73–77/15kyrs, or a 195year return period) and X (25–29/15kyrs, or a 517year return period) recurrences are observed near the South Alkyonides fault system, which dominates the strong ground motions hazard in the western part of the Attica mainland.

Seismic risk assessment and mapping at different levels

Earthquakes incur the greatest damage compared with all the other natural deleterious occurrences; when occurring in industrialized and densely populated regions, they can prove devastating. In the Russian Federation, we have more than 20 million people living in regions of moderate and high seismicity. The areas that are hit by earthquakes, with events of intensity VII (MMSK-86 scale) or greater occurring, make up approximately 20% of Russia’s area. The present paper addresses the methodological procedures of risk assessment and databases used for risk computations at different levels. The examples of seismic risk assessment and mapping at different levels: country, region and urban, are given. Special attention is paid to information and web technologies used for verification data on built environment inventory and vulnerability.