Low Seismic Hazard Research Articles

Analyzing the dependency of earthquake insurance premium on the intensity measure used in probabilistic seismic hazard analysis and fragility curves

Considering the uncertainties associated with earthquake, seismic response of structures, damage caused by the response and the repair costs, determining Earthquake Insurance Premium (EIP) is a challenging task that requires a framework for modeling all inherent risks. Most of the models proposed for EIP determination have two basic components. The first component indicates the probability of seismic hazard (generally obtained from the probabilistic seismic hazard analysis), and the second component indicates the probability of occurrence of a given damage to the structure with respect to different seismic hazard levels (generally obtained from the fragility curves). These two components are interconnected through an intermediate parameter, known as the Intensity Measure (IM), which is of great importance in calculations and has hardly been considered so far. In this study, the dependency of EIP on the IM used in the probabilistic seismic hazard analysis and the fragility curves is analyzed. To this end, the EIP was determined for five types of buildings at low, medium and high seismic hazard levels using two IMs (peak ground acceleration and first mode spectral acceleration). The results of this study warn that the EIP can be highly dependent on the IM, so that for all studied structures, the EIP determined based on peak ground acceleration at a high seismic hazard level is nearly three times as many as the one determined by the first mode spectral acceleration. A significant finding is that when the first mode spectral acceleration is used as the IM, the ratio of EIP at different seismic hazard levels closely matches the ratio of IM at the same levels. This result can be valuable in developing insurance codes and regulations. However, this is not the case for the currently used IM, i.e., peak ground acceleration.

Uniform deformation distribution of structures at different seismic hazard levels using endurance time method

This paper evaluates the application of the endurance time method in the optimum performance design of structures using the uniform deformation theory. The structures used in this study include shear-building systems with 5, 10, and 15 stories, and steel moment-resisting frames with 3, 7, and 12 stories. Initially, shear-building systems are optimized to have uniform story ductility ratios at low, moderate and high seismic hazard levels separately using three sets of ground motion records and a compatible series of endurance time acceleration functions. The effectiveness and accuracy of the endurance time method are assessed by comparing lateral force distribution obtained from this method with its corresponding attained from ground motion records. Moreover, as the number of stories and target ductility increases, the compatibility of these two methods improves. However, it is found that the optimum structure at one seismic hazard level does not necessarily lead to the optimum structure at other seismic hazard levels. Next, by adding dampers with gap to the systems, a procedure is suggested to optimize these structures at different seismic hazard levels simultaneously. These dampers are activated at moderate and high seismic hazard levels. Finally, similar optimization algorithm is used for steel moment-resisting frames to make their story drift ratios or plastic hinge rotations uniform along the height at different seismic hazard levels. Results show that combining endurance time method and uniform deformation theory leads to a promising optimization procedure that can significantly reduce computational costs with reasonable error.

Performance-based Analysis of Building Structures in Various Earthquake Zones

The structural design of an eight-story building was examined to determine its performance in resisting ultimate loads. This was necessary for applying the building design in Indonesian regions with low to high seismic hazard levels. Studies have indicated that pushover analysis is suitable to assess the capacity of building structures against earthquake loads. However, as the structural design of each building produces its nominal strength, performance analysis must always be conducted. This study aimed at comparing the structural performance of buildings in regions with low, medium, and high seismic hazards, represented by the cities of Palembang, Jakarta, and Palu, respectively. A performance-based analysis was conducted using the pushover method to obtain the performance points. The responses of the building structures were the base shears, floor drifts, and inter-story drifts. The structural performance levels in the three regions were between immediate occupancy and life safety or were categorized as damage control, indicating minor damage. Because the structures exhibited high stiffness and ductility, they resisted the ultimate forces up to the damage control performance level in all regions. The greatest lateral drifts of 79.744 mm and 51.656 mm in the X- and Y-axis directions, respectively, occurred in Palu’s high seismic hazard region. The lowest lateral drift occurred in Palembang’s low seismic hazard region, in the X- and Y-axis directions of 59.401 mm and 38.378 mm, respectively.

Partially grouted masonry walls with different horizontal reinforcement types: North American-compliant experimental performance for low seismic risk areas

The type of horizontal reinforcement can play a major role in the shear response of partially grouted (PG) masonry walls, particularly in the damage pattern and the post-peak behavior. Bond beam reinforcement and bed joint reinforcement are the two reinforcement types most commonly used in practice; however, there is a lack of comparative studies between these two reinforcement strategies. To advance knowledge on this matter, this paper presents the results of an experimental study made up of 4 full-scale walls tested under cyclic lateral loading. Two height-to-length aspect ratios (H/L = 1.0, 1.86) and two reinforcement types per aspect ratio were considered. These walls were designed to reflect practical details and construction practices for PG walls in low seismic hazard areas.Lateral load tests showed that the peak strength of walls with similar aspect ratios had no significant difference regardless of the reinforcement type used. Bed-joint reinforcement proved to be a vital option as a shear reinforcement for controlling the crack width. The preliminary assessment of in-plane strength prediction equations for PG walls revealed that the general flexural analysis method provides a satisfactory estimation of flexural strength. In contrast, code-based equations had a highly conservative prediction of shear strength when imposing the upper limit. In addition, the Canadian Standards Association (CSA) and The Masonry Society (TMS) equations used to predict the in-plane shear strength had a noticeable discrepancy in the contribution of the equation's parameters, particularly in the axial stress, horizontal reinforcement, and the upper limit, which highlighted the need to revise and reconsider the contribution of each design parameter used by these expressions.

First paleoseismic data from the Balkan Range

The normal faults along the Balkan range front integrate great tectonic relief, prominent basin-and-range morphology, historic seismic quiescence, and ongoing dilatation rate varying near zero. The official standards prioritize the instrumental seismicity in a random model of earthquake occurrence, and the region is assessed at low seismic hazard levels. The need of geologic data on earthquake occurrence motivated us to excavate the first paleoseismological trench in the Balkan Range. We trenched the Zlatitsa normal fault, which occupies the westernmost position within a zone of localized strain along the Central Balkan Range. The trench exposure revealed two surface-rupturing earthquakes generated at a long-term slip rate lower than 0.04 mm/yr, probably about 0.02 mm/yr for the past 42 thousand years. A stratigraphic hiatus between the earthquake records, coincident with the Last Glacial Maximum, results in large uncertainties in the estimated inter-event time, yielding 13.2–33.4 kyr (95 % confidence interval). The new data suggest that the strain is released by regionally distributed faulting. The Zlatitsa fault may form spatial clusters with the neighboring faults, analogous to the two M6.8–7.1 earthquake pairs in 1904 and 1928, south the studied location. The time elapsed since the most recent earthquake on the Zlatitsa fault is 1–15 % from the duration of the previous seismic cycle. The geodetic dilatation rate in the fault vicinity most likely exceeds several times the paleoseismic dilatation rate. However, the geodetic rate eastward from the fault is nearly identical to the paleoseismic rate obtained in the trench. Assuming exponentially decreasing fault reloading, the Zlatitsa fault may still undergo rapid stress restoration, whereas the time elapsed since the most recent earthquakes on faults to the east may be longer than the corresponding relaxation time.

Learning from the Past: Parametric Analysis of Cob Walls

In this paper, the results obtained from a series of parametric analyses, where the influence that geometric and mechanical parameters have in the structural response of existing vernacular cob walls within an Irish context, are presented. A design of experiments using central composite designs was implemented along with analysis of variance following two computational approaches, namely, the finite element method and kinematic limit analysis. As results, a series of response surfaces and parametric equations with which it is possible to compute safety factors and collapse multipliers (within the range of values studied) are provided. Based on the results obtained, it could be concluded that traditional cob walls in Ireland are very robust. Relatively high acceleration values, unlikely to happen in a low seismic hazard region such as Ireland, would be needed to start the collapse mechanisms studied or cause yielding in typical vernacular cob walls. Furthermore, the equations generated with the refined regression models can be used by practitioners as a first approach to estimate the safety levels of existing cob buildings with similar characteristics.

Seismic reliability of Italian code‐conforming bridges

AbstractSeismic reliability assessment of selected bridge structures code‐conforming with respect to the current Italian practice is carried out. Two viaducts, tall and shallow, and two highway overpasses, with traditional seat‐type or integral abutments, are considered. Each structure is ideally placed at three reference sites, that is, Milan, Naples and L'Aquila, characterised by low, moderate and high seismic hazard, respectively. At each site, a soil profile representative of typical local conditions is defined for foundation design, site response analysis and soil‐structure interaction modelling. Probabilistic seismic hazard is used in conjunction with multiple‐stripe non‐linear dynamic analysis, featuring conditional‐spectrum compatible ground motions, to establish the failure rate with respect to two purposely defined and functionality‐related performance levels. It is confirmed the decreasing seismic reliability with increasing design seismic action, already observed for other structural types, and it is shown that integral abutment overpasses tend to be more reliable than traditional ones, even seismically isolated ones. The results are of larger interest given the closeness of the Italian code to the Eurocode.

A risk-targeted approach for the seismic design of bridge piers

Designing a structure to resist earthquakes by targeting an explicit failure risk has been a key research topic over the past two decades. In this article, a risk-targeted design approach is developed for circular reinforced concrete bridge piers, based on a probabilistic optimization procedure aimed at minimising the design resisting moment at the pier base. In order to reduce the computational effort, a surrogate model is developed to describe the influence of two key design parameter (i.e., the pier diameter and the longitudinal reinforcement ratio) on the structural behaviour and performance. The proposed approach is applied in a case study for Italy for target mean annual frequencies of failure selected according to European codes using a probabilistic seismic hazard assessment for average spectral acceleration across a wide range of structural periods. The variation in the design parameters across Italy is considerable because of the large variation in seismic hazard. It is found that in areas of low seismic hazard the level of seismic design required is near the minimum allowed by Eurocode 8 in terms of reinforcement ratio. In areas of the highest seismic hazard much higher reinforcement ratios and pier diameters are required to meet the risk targets. If both pier diameter and longitudinal reinforcement ratios are considered as design parameters then the optimisation procedure may mean adjacent sites have significant different pairs of these parameters as the target can be reached in multiple ways. This problem can be solved by fixing one parameter and optimising the other.

Potential seismic landslide hazard and engineering effect in the Ya’an-Linzhi section of the Sichuan-Tibet transportation corridor, China

The Sichuan-Tibet transportation corridor is located at the eastern margin of the Qinghai-Tibet Plateau, where the complex topography and geological conditions, developed geo-hazards have severely restricted the planning and construction of major projects. For the long-term prevention and early control of regional seismic landslides, based on analyzing seismic landslide characteristics, the Newmark model was used to carry out the potential seismic landslide hazard assessment with a 50-year beyond probability 10%. The results show that the high seismic landslide hazard is mainly distributed along large active tectonic belts and deep-cut river canyons, and are significantly affected by the active tectonics. The low seismic landslide hazard is mainly distributed in the flat terrain such as the Quaternary basins, broad river valleys, and plateau planation planes. The major east-west linear projects mainly pass through five areas with high seismic landslide hazard: Luding-Kangding section, Yajiang-Xinlong (Yalong river) section, Batang-Baiyu (Jinsha river) section, Basu (Nujiang river) section, and Bomi-Linzhi (eastern Himalaya syntaxis) section. The seismic action of the Bomi-Linzhi section can also induce high-risk geo-hazard chains such as the high-level glacial lake breaks and glacial debris flows. The early prevention of seismic landslides should be strengthened in the areas with high seismic landslide hazard.

Fault structure and segmentation of the Punta Montalva Fault in southwestern Puerto Rico using high-resolution digital elevation models

The Punta Montalva Fault is an active fault that slipped during the 2019–2023 Puerto Rico seismic sequence. It lies in southwestern Puerto Rico within the ∼250-km-wide deformation zone of the North American-Caribbean plate boundary. The fault cuts Miocene limestone and contains surface features that suggest left-lateral displacement. Previous work suggested that the fault connects with the North Boquerón Bay Fault for a length of 33 km and poses a large seismic hazard. However, not much is known about the structure, segmentation, and spatial extent of the fault as it is obscured under thick vegetation. This study used high-resolution topographic data to map the structure, segmentation, and spatial extent of the fault. The results would allow us to better assess the seismic potential of the Punta Montalva Fault by constraining its spatial extent and how strain has been accommodated. A 0.5 m resolution bare-earth digital elevation model (DEM) derived from a 2018 airborne LiDAR survey and another 1 m resolution 2018 DEM showing shallow bathymetry were used to map the Punta Montalva Fault. High-resolution mapping revealed that the Punta Montalva Fault is comprised of three main fault segments on land, a possible additional scarp, and three fault scarps on the seafloor to the SE. No evidence suggests the Punta Montalva Fault extends further NW of Punta Montalva into La Parguera in Lajas. The DEM revealed that the fault cuts a shallowly dipping sedimentary sequence of the Ponce Limestone that has karst topography in places. On land, the fault is conspicuous where it forms scarps, drags and cuts sedimentary layers, and forms a duplex structure with a predominantly left-lateral offset. A left-lateral offset of an intermittent stream has been refined to 133.6 ± 7.3 m. The fault scarps along a marine shelf strike E-W and show a maximum normal offset of 4.8 m. Another sub-parallel fault scarp in the seafloor strikes NW-SE and displays a left-lateral offset of 98.3 m. The total length of the fault segments is ∼2.67 km long. The surface segmentation suggests that the fault would have a lower seismic hazard than if it were continuous and connected to the North Boquerón Bay Fault. However, if the Punta Montalva Fault is continuous beneath the surface, its total fault length would be approximately 7.97 km long and would pose a larger seismic hazard than that suggested by the surface segmentation. Strike-slip, folding, and normal offset suggest that the area is being deformed by transtentional deformation, which supports seismic analyses and tectonic models.

Seismic response and fragility evaluation of circular tunnels in the Himalayan region: Implications for post-seismic performance of transportation infrastructure projects in Jammu and Kashmir

The expanding infrastructural projects together with the prior historical records of significant earthquakes including the deadliest 2005 Kashmir earthquake in the Himalayan region, urge to assess the seismic vulnerability and risk of Jammu and Kashmir. This paper attempts to assess the seismic vulnerability of circular tunnels using the fragility function for various seismic environments. To accomplish this, the seismic performance of tunnels is quantified for each hazard zone with a diverse typology and seismic scenario. Microzonation results aided in defining the four hazard zones based on seismic severity. Zone A, B, C, and D are seismic zones with severe, high, moderate ad low Seismic Hazard Indexing (SHI). Tunnel performance is evaluated for each hazard zone, and empirical correlations for damage indices are defined. For Zone A, the fragility curves presented for minor, moderate, and extensive damage states for both shallow and deep tunnels appear to be extremely catastrophic. For various slippage conditions, the variation of flexibility and racking ratios for tunnels with shallow and deep overburden depths is significant. The proposed fragility curves are used to evaluate the seismic risk of a roadway network that includes A, B, and C routes that pass through Jammu. The risk matrices and probability function revealed that all tunnels on Route A are extremely vulnerable to damage. Extensive portal collapse and tunnel lining failure will render this route inoperable during the post-seismic phase. The developed empirical correlations, fragility curves, and risk matrices will serve as a ready-to-use tool for tunnel design engineers working on any Himalayan infrastructure project.

Seismic Risk Assessment of Nagpur City using the Geographic Information System

Earthquakes are the major threat to mankind accounting for almost half of the fatalities brought about by all of the natural hazards and desert their traces in societies for years. It is well known that seismic risk cannot be eliminated but minimized. Risk studies lay down the roadmap to prepare and minimize the aftermath of any disastrous event. Geographic Information System (GIS) has been proved as an effectual tool for seismic risk assessment study. This study presents the seismic risk assessment of Nagpur city using the GIS framework. Albeit per Indian Standard (IS) 1893-2016 [1] seismic zonation of Nagpur city comes under zone II (relatively low seismic hazard zone), the seismic risk being a combination of hazard, elements at risk and, vulnerability cannot be denied. Similar to other Indian cities the city of Nagpur had a heterogeneous development pattern. Even though Nagpur city is municipalized in well distributed wards, many intra wards distributions show housing clusters of different socioeconomic status. Therefore, using the satellite imagery different socioeconomic housing clusters were identified and mapped in the ArcGIS platform. Six socioeconomic clusters were identified using satellite imagery for Nagpur. From the field survey of randomly selected typical clusters, 14 prevailing Model Building Types (MBTs) were identified. Census data were used to find the population density and its distribution throughout the city. Seismic hazard has been estimated from IS 1893-2016 [1] as well as using the probabilistic hazard map of NDMA [2]. Selected MBTs were assessed for their seismic vulnerability, seismic risk in terms of casualties and damage is calculated. Finally, thematic maps showing damages arrived from the various approach are shown and discussed.

MICRO-ZONATION STUDY OF POTENTIAL SEISMIC HAZARDS BASED ON PEAK GROUND ACCELERATION (PGA) VALUE IN THE NORTH KONAWE OFFICE AREA

The purpose of this study was to determine the potential for seismic hazard based on the peak ground acceleration value in the North Konawe office area. This study uses the HVSR method to obtain the dominant frequency, amplification factor, dominant period, seismic vulnerability index and Peak Ground Acceleration. The results obtained from the microzonation of the distribution of the dominant frequency value with a high category were found at 5 measurement points, the amplification factor with a low category was found at 1 measurement point, the dominant period with a low category was found at 6 measurement points and the seismic vulnerability index with a low category was found at 5 points. measurement. Overall the research area is included in the level of seismic hazard risk, not high potential but in the low category. While the microzonation of the distribution of PGA values ​​obtained values ​​ranging from 23,2381-23,3231 gal which belong to the low seismic hazard risk level. Where it can be described in this area the earthquake that occurred can be felt by many people but caused damage. The light objects that were hung swayed and the windows shook. So it can be concluded that this research area is included in the category of low seismic hazard level

Elusive active faults in a low strain rate region (Sicily, Italy): Hints from a multidisciplinary land-to-sea approach

Low Strain Rate regions (LSRrs), i.e., areas undergoing tectonic deformation at rates of 1 mm/yr or less, often host important cities and highly vulnerable anthropogenic assets, and due to their subdued topography and relatively infrequent seismicity, are often considered low seismic hazard areas. Despite this, infrequent but high-magnitude earthquakes in such regions suggest that identifying active structures in the LSRr is one of the primary challenges for both the scientific community and modern societies. In such regions, one of the main issues in identifying active faults is the lack of valuable outcrop data due to erosional/sedimentation rates overwhelming the fault deformation, causing the hidden morphological signature of the tectonic structures.This work proposes a multidisciplinary approach designed to detect active geological structures and their related deformation in such areas. Our approach consists of quantitative morphotectonic, offshore and onshore tectonostratigraphic and GNSS joint analyses. To test this approach, we selected as a natural laboratory the partially offshore northern Sicilian LSRr (southern Italy) in the coastal sector located between the two major cities of Palermo and Termini Imerese. This area includes the compressional structures of the northern sector of the Apennine-Maghrebian fold and thrust belt, presently accommodating the slow Africa-Europe plate convergence.The main results we achieved are 1) new evidence of active tectonic deformation in this region; 2) the 3D modelling of two NNW-trending active faults; 3) the slip rate of a segment of the westernmost of the two detected faults; 4) a newly recorded relative GNSS velocity field; 5) a new morphotectonic map and morphotectonic evolution model of the study area. Our multidisciplinary approach allowed us to shed new light on the active tectonic framework of a slowly deforming area that crosses the physical limit of the coastline.

Analysis of Soil Acceleration in The Mentawai Region with The Method Probabilistic Seismic Hazard Analysis (PSHA)

The Mentawai Islands are one of the areas that are active in seismicity. An earthquake measuring 7.2 on the Richter scale on October 25, 2010 resulted in many casualties and material losses. Many buildings collapsed and facilities were damaged so that space managers needed a seismic hazard map to be able to organize the space by considering the disaster aspect. This prompted researchers to conduct research aimed at making seismic hazard maps and knowing the level of earthquake hazard in the Mentawai region. Seismic hazard maps are useful in planning earthquake-resistant buildings and can describe the effects of earthquakes at a location which will help in anticipating community preparedness and earthquake disaster mitigation efforts. Seismic hazard data processing uses the Probabilistic Seismic Hazard Analysis (PSHA) method. PSHA is based on earthquake parameters that produce the largest ground motion. The magnitude of the intensity at a location due to an earthquakein the earthquake source area with a magnitude of M and a distance of R, the attenuation function can be used. The attenuation functions in this study are Joyner-Boore (1997) and Young et al (1997). This type of research is descriptive, namely by collecting NEIC/USGS earthquake catalog data for the period 1950 - 2021 with M 5 SR.The results of this study indicate that the area of ywhich has a high level of seismic hazard is found in the Siberut area with a maximum PGA range of 1.17 g - 3.70 g. The area with a low seismic hazard level is the Pagai area with a PGA range of 0.80 g - 2.86 g. This result represents a 10% chance of being exceeded in 50 years.

Comparison of Various Types of Seismic Hazard Assessment and their Influence on Structural Vulnerability

This work sought at enhancing techniques for the assessment of seismic risk in order to understand displacement effects and impacts of different seismic hazard estimation techniques on structural vulnerability. The analysis is useful because the number of earthquakes around the world is on the rise, and there is a necessity to eliminate the potential threat. Weighted Average of Ground Motion intensities was used to determine hazard parameters, along with PSHA and DSHA. The information regarding seismicity was collected from the regional networks and catalogs with the help of geotechnical investigation for site characteristics. An assessment of structural resilience was accomplished with building inventories and retrofit projects data with the help of FEA for computational modeling. The degree of earthquake was recorded to be from 4. 5 to 7. 5 Mw, with PGA ranging from 0 to 0. 2 to 0. 3g. During preliminary screening, Sites were ranked into high PSA and low PSA divides as well as Low Seismic Hazard and Medium to High Seismic Hazard. These retrofitting measures such as base isolation and strengthening further improved performance of buildings, in that they reduced peak drift ratios by up to 50% and, base shear force capacity by 30% of average value. The Effectiveness Index of retrofitting work varied from 0. 732 to 0. 912, from which one can draw the conclusion concerning appreciable enhancements of earthquake resistance. The study thereby laid a foundation to prove that it is possible to reduce the seismic risk by using the advanced hazard analysis methods and based on these analyses, some systematic retrofit interventions are effective enough in achieving the objective of sustainable urban development. The conclusions derived in this paper present quantitative information relevant for understanding actions toward earthquake prevention in vulnerable territories.

Household earthquake preparedness in Oklahoma: A mixed methods study of selected municipalities

BackgroundInduced seismicity has increased in prevalence in the central United States following an increase in hydraulic fracturing and the resultant disposal of wastewater back into the Earth's crust. At least 22 out of 77 counties in Oklahoma are affected. Ranging from low to moderate magnitudes, induced earthquakes (IE) can result in property damage, property value decrease, and detrimental personal wellness. MethodsIn this study, we use a mixed methods design to investigate the earthquake preparation actions of the residents of Cushing, OK and Pawnee, OK, two areas with high rates of moderate magnitude IEs, and to understand what factors influence the earthquake preparedness decisions of people living with IE in Oklahoma. ResultsThrough the quantitative component of the study, we find the study population unprepared for earthquakes. We found no statistically significant differences in earthquake preparedness between community members who experienced IE damages and those who did not. In the qualitative component, five themes explaining the lack of preparedness emerged: lack of earthquake experience; lack of IE preparedness knowledge; difficulty preparing for multiple hazards; resentment toward preparing for an induced hazard; and IE damages should not be the responsibility of impacted residents. ConclusionAs deep wastewater injection continues in usage, public health interventions for seismic hazards must be adapted to address the needs of communities affected by the outcomes. Community earthquake preparedness education and involvement are needed to mitigate the outcomes of induced seismicity in areas of low natural seismic hazard.

Earthquake recurrence characteristics for potential seismic zones in the southern Red Sea region and their hazard implications on Jizan city

This study aims to quantify seismic hazard assessments in the Jazan region. For this purpose, we determined earthquake recurrence parameters for potential seismic zones that may export risk to the region. A total number of ten seismic zones were identified based on the morphotectonic nature, seismic energy pattern, and previous studies. Estimates of the b-value varied from 0.74 to 1.42, reflecting different processes of tectonic activities. The maximum possible magnitudes (Mmax) of 5.9 ± 0.3 to 8.3 ± 1.1 are anticipated to be occurred in the region between 48 and 2090 years with annual probabilities of 13%, 23%, and 36% in 25, 50, and 100 years of life, respectively. Finally, the maximum expected magnitudes obtained from this study were used in cooperation with five alternative attenuation relationships to predict peak ground accelerations. The seismic hazard map of 84% was produced at hard rock using logic tree uncertainties, showing a high seismic hazard alongside the coastline shores while a low seismic hazard extended inside the Arabian Shield that is assumed to have a stable continental crust. The response spectra at hard rock in Jizan city showed maximum PGA values corresponding to spectral frequencies of 2–5 Hz, implying that high-frequency vibrations may have an impact on building structures.

The Rise, Peak and Decline of the Seismic Hazard Related to Hydraulic Fracturing Activities in the Duvernay Play, Fox Creek Area, Alberta

AbstractWe analyze the temporal evolution of the induced seismicity related to hydraulic fracturing activities in the Duvernay Formation, near Fox Creek, Alberta, Canada. For this analysis, we estimate annual Gutenberg‐Richter parameters, ‐ and ‐ values, and then calculate the annual likelihood of earthquakes greater than magnitude from 2014 to 2020. The seismic hazard near Fox Creek has consistently decreased since 2015, from a 95% probability of an earthquake greater than magnitude in 2015 to 4% in 2019 and less than 1% probability in 2020. The induced seismicity in Fox Creek is characterized by two actively seismic regions with distinctive features: (a) an Eastern region (∼220 events ) with lower b‐values and higher hazard; (b) a Western region (∼210 events ) with higher b‐values and lower seismic hazard. In contrast, extensive regions where hydraulic fracturing is performed, particularly East of the seismic cluster, remain non‐seismogenic. The overall decreasing seismic hazard, which contrasts with increasing operator activity, can be associated with (a) the intensification of hydraulic fracturing operations toward areas less susceptible to induced seismicity and (b) the reduction of seismic activity in the Eastern region, which exhibits the highest seismic hazard. We also find evidence of a minimum annual injection volume required to trigger induced seismicity in both the Western and Eastern regions. The minimum injection threshold increases over the years, implying increasingly successful mitigation strategies, likely due to regulatory implementations in the area, which has led the operators to exercise precaution in regions with significant seismic hazard and adapt treatment strategies to avoid triggering moderate magnitude size events during hydraulic fracturing stimulations.

Seismic isolation: A pathway to standardized advanced nuclear reactors

Standardizing advanced nuclear reactors is a pathway to substantially reducing their overnight capital cost and achieving parity with other power sources, including renewables and fossil fuels. The seismic load case has thwarted standardization of nuclear power plants because site-specific seismic hazard and local near-surface geology has triggered soil-structure-interaction analysis, design, equipment qualification, regulatory review, and licensing, ensuring that each build is different. To achieve standardized or site-independent certified advanced reactor designs, the impact of the seismic load case on the engineering and construction cost and time must be substantially mitigated. Seismic isolation is a mature technology that has been used for more than 30 years in non-nuclear sectors to substantially reduce earthquake demands in buildings and other infrastructure. In this paper, seismic isolation is used to enable standardization of advanced reactor designs, aimed at the complete re-use of a site-independent, certified design and repeated procurement of safety-class equipment. A pathway to standardized designs using seismic isolation is demonstrated for two fundamentally different advanced reactors: a molten salt reactor and a high temperature gas reactor. Each reactor building is equipped with three specialized pieces of safety-class equipment, namely, a reactor vessel, a steam generator, and a control rod drive mechanism housing that is attached to the reactor head. Analysis is performed per ASCE and ASME standards to design the buildings and the equipment for two base conditions: conventional (fixed base) and base isolated. The impact of the seismic load case is characterized for the reinforced concrete walls in the buildings and for the equipment, measured using vessel wall thickness and horizontal accelerations. The analysis results show that the fixed-base buildings, designed for a site of low seismic hazard (peak ground acceleration, PGA = 0.15 g) could be constructed at a site of much greater seismic hazard (PGA = 0.7 g) if seismic base isolation is employed. Importantly, the scope of the site-specific analysis, design, and qualification would be limited to the seismic isolators and the isolated substructure, drastically reducing plant-specific engineering, review, and licensing, and time to construction start. Regulatory challenges and opportunities with standardized reactor designs are identified.