Areas Of Low Seismicity Research Articles

Multistep procedure for estimating non-linear soil response in low seismicity areas—a case study of Lucerne, Switzerland

SUMMARY The impact of non-linear soil behaviour on seismic hazard in low-to-moderate seismicity areas is often neglected; however, it may become relevant for long return periods. In this study, we used fully non-linear 1-D simulations to estimate the site-specific non-linear soil response in the low seismicity area, using the city of Lucerne in Switzerland as an example. The constitutive model considers the development of pore pressure excess and requires calibration of complex soil models, including the soil dilatancy parameters. In the absence of laboratory measurements, we mainly used the cone penetration test data to estimate the model variables and perform inversion for the dilatancy parameters. Our findings, using Swiss building code-compatible input ground motions, suggest a high probability of strong non-linear behaviour and the possibility of liquefaction at high ground motion levels in the case study area. While the non-linearity observations from strong-motion recordings are not available in Lucerne, the comparison with empirical data from other sites and other methods shows similarity with our predictions. Moreover, we show that the site response modelled is largely influenced by the strong pore pressure effects produced in thin sandy water-saturated layers. In addition, we demonstrate that the variability of the results due to the input motion and the soil parameters is significant, but within reasonable bounds.

Assessing network-based earthquake early warning systems in low-seismicity areas

Earthquake early warning (EEW) technology, designed to alert the public of earthquake risks after initial P-wave detection but before the onset of strong tremors, has developed rapidly. Methodologies from various fields are combined in EEW systems to estimate earthquake locations, magnitudes, and expected intensities based on the initial P-wave data. These systems operate automatically because prompt responses are required. However, as no common evaluation framework for EEW system verification exists, potentially divergent evaluations from reviewers or countries could ensue. Moreover, evaluating EEW systems is more complicated when the target area does not experience frequent earthquakes. We aimed to establish a guidance review process for low-seismicity areas to ensure reliable and stable integrated EEW system operation. We incorporated management aspects through actual system operator surveillance and designed an EEW assessment process based on feedback from our surveys. Using this approach, we created a comprehensive and well-informed evaluation process that considers the diverse perspectives of experts involved in EEWs. Our proposed assessment method allows for a uniform and consistent evaluation process, regardless of changes in the methods or technologies used by EEW systems. The method aims to guide EEW system assessments in low-seismicity areas.

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.

Experimental study on the seismic performance of prefabricated frame piers

Prefabricated assembly technology can speed up the construction process and is widely used in the construction of urban bridges. However, research on the seismic performance of prefabricated frame concrete piers is scarce, and the seismic performance of prefabricated frame concrete piers with different connection forms must be urgently evaluated. In this study, three prefabricated frame concrete piers with different connection forms–namely cast-in-place (CIP), grouted splice sleeve connection (PC-S), and grouted corrugated duct connection (PC-C)–were designed and fabricated. Through quasi-static testing, the seismic performances of the CIP, PC-S, and PC-C specimens were evaluated using bearing capacity, displacement ductility, stiffness degradation, energy dissipation capacity, etc. as evaluation indexes. Based on the plastic damage theory of concrete, a finite element model was established. The test results showed that all the three specimens experienced flexural failure, and their load–displacement hysteretic curves were similar in shape (i.e., shuttle-shaped). The bearing capacity and ductility coefficient of the PC-S specimen were 95.7% and 77.5% of the CIP specimen, respectively, and those of the PC-C specimen were 93.0% and 92.5%, respectively. The stiffness degradation trends of the three specimens were similar, but the PC-S specimen exhibited the largest initial stiffness, and the stiffness of the PC-S and PC-C specimens at failure was 86.0% and 95.7% of that of the CIP specimen, respectively. When the CIP specimen failed, the cumulative energy dissipation values of the PC-S and PC-C specimens were 16.7% and 14.2% lower than that of the CIP specimen, respectively. The numerical simulation curves fitted well with the test curves, which verified the accuracy of the test results. The seismic performances of two kinds of the prefabricated bridge piers were close to the CIP specimen. When the strength of connectors and sealing material meet the requirements, prefabricated frame concrete piers can be preferentially selected for medium and low seismic areas.

Seismic performance of precast double-column pier with UHPC-filled socket connections

Precast piers have been extensively investigated and applied in low seismic intensity areas, owing to the faster construction speed, limited traffic interruption, and environmental friendliness. However, few studies and engineering practices of the precast double-column piers (PDPs) located in high-intensity seismic areas have been reported. Therefore, in this study, a novel socket connection filled with ultra-high-performance concrete (UHPC) was proposed for the PDPs. The socket connections with concrete filled steel tube (CFST) are used to enhance the strength of the column-cap beam joints, at the same time the socket connections with the tooth-shaped shear keys are adopted at the column-footing joints to reduce the required anchorage length. The PDP with a scale ratio of 1:3 was constructed and then tested under the quasi-static load to investigate its seismic performance. Finally, a simplified analytical model of the socket connections was proposed based on the concept of the elastic foundation beam. The test results demonstrate that the damage of the specimen PDP was mainly concentrated at the bottom of the columns, and the damage at the damage ends of the PDP specimen was severer than that of the cast-in-place (CIP) specimen. The load-bearing capacity of the PDP is slightly higher than that of the corresponding CIP specimen, while the energy dissipation and displacement ductility of PDP are slightly smaller than those of the CIP specimen. The proposed model could accurately and efficiently capture the hysteretic behavior of the proposed PDP with socket connections.

Improving Out of Network Earthquake Locations Using Prior Seismicity for Use in Earthquake Early Warning

ABSTRACTTimely alerts sent through earthquake early warning (EEW) programs allow those alerted to take protective actions to mitigate their risk from potentially damaging shaking. Over the past few years, ShakeAlert, the EEW program focused on the west coast of the contiguous United States, has grown, alerting communities within California, Oregon, and Washington about earthquakes where damaging shaking is expected. ShakeAlert uses a set of algorithms including the point-source algorithm, earthquake point-source integrated code (EPIC), to determine the location, magnitude, and origin time of potential earthquakes. Although EPIC produces low-latency and low error solutions for many events originating within the seismic network on land, numerous recent small earthquakes rupturing offshore of northern California have EPIC location solutions with high error (>50 km compared to USGS locations). Because most events are occurring offshore, there is a limited number of stations that can trigger and contribute information in a timely manner for use in EEW. To better constrain location solutions in this region, we propose to include information about contemporary past seismicity into EPIC’s grid-search algorithm through a Bayesian framework. This prior information layer downweights high error locations where EPIC’s proposed event location coincides with an area of low prior seismicity in preference for locations with a similar level of data fit that also have higher past seismicity. This addition to EPIC lowers the mean location error offshore northern California from 58 to 14 km.

Impact of site condition on Arias intensity and Cumulative absolute velocity: application for low seismicity areas

Impact of site condition on Arias intensity and Cumulative absolute velocity: application for low seismicity areas

Seismic vulnerability of gravity load design r.c. buildings of 1960s in low seismic areas

In recent years, there has been a substantial increase in the issues of assessing the seismic vulnerability of existing structures and reducing seismic risk in Italy. Most of the buildings in Italy dates back to 1950s-60s and are Reinforced Concrete buildings designed only to vertical loads (GLD). In some cases, these buildings are located in areas that were defined as non-seismic zones in previous seismic classification of the national territory. Nowadays, in a whole seismic country the study of the seismic vulnerability of this type of buildings represents a really interesting issue.In this paper the seismic vulnerability of a building of the Olympic Village of Luigi Moretti in Rome has been evaluated, as representative case, originally designed to counteract only vertical loads. This valuable solution by Moretti respects the “five points of modern architecture” by Le Corbusier. It was built on the occasion of the XVII Olympics in 1960 with the aim of hosting the participating athletes. It is characterized by resisting frames only in transverse direction, as occurred for Le Unitè d'Habitation by Le Corbusier.

Lower and Upper Plate Controls on Crustal Seismicity in the Southern Central and Patagonian Andes

AbstractWe analyze crustal seismological records to assess the origin of the variable seismic activity along the southern Central and Patagonian Andes (30°–55°S), an area associated with latitudinal changes in the lower‐plate geometry, upper‐plate deformation, and topography. We carried out a statistical analysis of the seismicity records at crustal depths of 0–50 km from an updated earthquake catalog. Studying the seismicity by its area covered, depth, latitude, and time, this analysis reveals a consistent and drastic decrease in the number of earthquakes south of 38.5°S. We note that the low seismicity area is spatially correlated with a thin, hot, and weak (at least in the forearc region) upper plate and the subduction of a young/warm lower plate with short slab depths (∼150–400 km) beneath Patagonia. Notably, the reduced upper plate seismicity is mimicked at depth by a similar decrease in lower plate seismicity associated with the presence of relatively shallow slabs south of 38.5°S. This observation allows us to suspect a genetic connection between lower plate properties and the striking reduction in the upper‐plate seismicity. We tentatively suggest that the young/warm and short Nazca and Antarctic subducting plates, left after Neogene slab detachments, modified the thermomechanical upper plate structure, triggering the drastic decrease in crustal earthquakes. This process was likely aided by an inherited thin continental margin. This study reveals that slab detachment in non‐collisional settings can impact upper‐plate seismicity.

Analysis of Local Site Effects in the Međimurje Region (North Croatia) and Its Consequences Related to Historical and Recent Earthquakes

The Međimurje region (North Croatia), situated between the Drava and Mura rivers with a slightly elevated hilly area, can be generally characterized as a low-seismicity area. However, macroseismic observations from historical and recent earthquakes indicate that some localities in this region are more prone to damage than others. Significant damage and the observed higher intensities in the Međimurje region after the historical earthquakes of 1738 MLm5.1 (Međimurje) and 1880 ML6.3 (Zagreb), and events that occurred in the instrumental era, 1938 ML5.6 (Koprivnica), 1982 ML4.5 (Ivanec), and the most recent 2020 ML5.5 Zagreb and 2020 ML6.2 Petrinja earthquakes, point to the influence of local site effects. There is a reasonable indication that these earthquakes involved several localized site effects that could explain the increased intensity of half a degree or even up to one degree at certain localities compared to macroseismic modeling for rock condition. To better understand the influence of local site effects in the Međimurje region, the single-station microtremor Horizontal-to-Vertical Spectral Ratio (HVSR) method for subsurface characterization was used. Based on individual measurements, microzonation maps were derived for the Međimurje region to better understand the behavior of ground motion and the influence of local site conditions in comparison to macroseismic intensities and past damage observations. Several local site effects could be interpreted as a main contribution to site amplification and resonance effects due to variations in deep soft-deposit thicknesses overlayed on hard deposits and directional variations in topographical areas that could localize earthquake damage patterns. Correlations of microtremor analysis with intensity observations from historical earthquakes as well with recent earthquakes could help to distinguish local site zones prone to the possible occurrence of higher earthquake damage from nearby and distant earthquakes.

Seismicity of Iraqi western desert and surroundings: As an example of continental intraplate seismicity

Seismicity of Iraqi western desert and surroundings was investigated using a complete and unified magnitude earthquake catalog covering the interval from 1900 to 2017. A marked rise in number of the events in the study area was observed after the year 2000 compared to the previous years. The magnitude of majority of the recorded events ranged from 2 to 3.5 Mw. The value of b-constant in frequency-magnitude relation is 0.7. The epicentral distribution shows that the western desert is aseismic to very low seismicity area compared to the surrounding regions. The epicenters were clustered in five seismogenic zones. The focal depths division of the events exhibits that majority of the earthquakes occur in the upper crust. A causal relation may be between the study area seismicity and the zones of weakness and /or stress condensation at the fault intersections.

Indicators of mantle control on the geodynamo from observations and simulations

There has been longstanding controversy about whether the influence of lateral variations in core-mantle boundary heat flow can be detected in paleomagnetic records of geomagnetic field behavior. Their signature is commonly sought in globally distributed records of virtual geomagnetic pole (VGP) paths that have been claimed to exhibit specific longitudinal preferences during polarity transitions and excursions. These preferences have often been linked to thermal effects from large low seismic velocity areas (LLVPs) in the lowermost mantle, but the results have been contested because of potential sensitivity to sparse temporal and spatial sampling. Recently developed time varying global paleofield models spanning various time intervals in 1–100 ka, three of which include excursions, allow us to complement assessments of spatial distributions of transitional VGP paths with distributions of minimum field intensity. Robustness of the results is evaluated using similar products from four distinct numerical dynamo simulations with and without variable thermal boundary conditions and including stable geomagnetic polarity, excursions and reversals. We determine that VGP distributions are less useful than minimum field intensity in linking the influences of thermal CMB structure to geographical variations in actual paleofield observables, because VGP correlations depend strongly on good spatial sampling of a sufficient number of relatively rare events. These results provide a basis for evaluating comparable observations from four paleofield models. The distribution of VGP locations provide unreliable results given the restricted time span and available data locations. Rough correlations of global distributions of minimum intensity with areas outside the LLVPs give some indications of mantle control during excursions, although the results for the eastern hemisphere are complex, perhaps highlighting uncertainties about the hemispheric balance between thermal and compositional variations in the lowermost mantle. However, access to other geomagnetic properties (such as intensity and radial field at the CMB) provides a strong argument for using extended and improved global paleofield models to resolve the question of mantle influence on the geodynamo from the observational side.

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.

Evaluating the Minimum Number of Earthquakes in Empirical Site Response Assessment: Input for New Requirements for Microzonation in the Swiss Building Codes

Site-specific hazard analyses and microzonation are important products for densely populated areas and facilities of special risk. The empirical amplification function is classically estimated using the standard spectral ratio (SSR) approach. The SSR simply consists in comparing earthquake recordings on soil sites with the recording of the same earthquake on a close-by rock reference. Recording a statistically significant number of earthquakes to apply the SSR can however be difficult, especially in low seismicity areas and noisy urban environments. On the contrary, computing the SSR from too few earthquakes can lead to an uncertain evaluation of the mean amplification function. Defining the minimum number of earthquake recordings in empirical site response assessment is thus important. We compute empirical amplification functions at 60 KiKnet sites in Japan from several hundred earthquakes and three Swiss sites from several tens of earthquakes. We performed statistical analysis on the amplification functions to estimate the geometric mean and standard deviation and more importantly to determine the distribution law of the amplification factors as a function of the number of recordings. Independent to the site and to the frequency, we find that the log-normal distribution is a very good approximation for the site response. Based on that, we develop a strategy to estimate the minimum number of earthquakes from the confidence interval definition. We find that 10 samples are the best compromise between minimizing the number of recordings and having a good statistical significance of the results. As a general rule, a minimum of 10 uncorrelated earthquakes should be considered, but the higher the number of earthquakes, the lower the uncertainty on the geometric mean of the site amplification function. Moreover, the linear site response is observed to be independent to the intensity of the ground motion level for the analyzed dataset.

Mechanical behaviour of multi-panel cross laminated timber shear-walls with stiff connectors

Multi-panel Cross Laminated Timber shear-walls with stiff vertical joints may represent a valuable structural solution for multi-storey timber buildings in low seismic prone areas. In this study, the opportunity of using shear-key connectors in the assemblage of stiff vertical joints as an alternative to short-spacing traditional dowel-type mechanical fasteners is evaluated. The mechanical behaviour of two types of stiff shear-key connectors is investigated through an experimental campaign conducted at joint and wall level. Shear tests were firstly carried out to determine the mechanical properties of panel-to-panel joints assembled with the shear-key connectors. The results are compared with those obtained from shear tests on joints with screwed connections (half-lap and spline joints). Full-scale shear-wall tests were then performed to determine the mechanical performances of the connectors at wall level. Joints with a single shear-key connector showed values of stiffness and strength comparable to those that would be obtained for vertical spline joints with approximately thirteen couples of 6 mm screws. The failure modes on the joints with shear-key connector were characterized by either a localized crushing in the wood or the shear failure in outer lamination of the CLT panels with no plastic deformation of the connectors.

Analysis and Research on Anti-seismic Scheme of Railway Simple Supported Beam Bridge

In order to improve the seismic performance of railway simply supported beam bridges, the seismic design schemes in different seismic intensity areas are compared and analyzed in this paper. The results show that the relative displacement of beam piers is too large when the simply supported beam bridge (≥ 0.3g) in high intensity earthquake area only adopts damping and isolation bearings. In order to reduce the displacement after earthquake, it is necessary to increase damping energy dissipation devices. Simply supported beam bridge in low intensity earthquake area (≤ 0.2g) adopt shock-absorbing isolation bearing. The cost of bearing will not increase, and the safety of bridge under earthquake will be greatly improved. It is recommended to adopt isolation design in low intensity seismic area.

The European Yield Model (EYM) for laterally loaded timber connections with smooth nails

ABSTRACT The European Yield Model (EYM) is a commonly accepted procedure to calculate the capacity of laterally loaded connections with dowel type fasteners. The standard procedure is specified in EC5 (EN 1995-1-1 2004) and uses characteristic values as input parameters for the calculation of characteristic values of the resistance of the connection. These characteristic values are the basis for an engineering design of structures. Nevertheless, there are situations, e.g. the design of a test set-up or a pushover analysis in earthquake engineering, when mean values of the resistance of a timber connection are needed. In this context, analytical equations and mechanical models were assessed on two levels by comparing theoretical values to experimental results. The first part of the research considered all the input parameters. The mechanical definition of the plastic moment proved to be more appropriate than the definition of a modified plastic moment according to EC5 for the determination of the yield moment of nails. On the other hand, it was confirmed that the embedment strength of Norway spruce softwood can be predicted reliably and slightly conservatively according to code regulations given by EC5. The definition for the withdrawal strength according to EC5 also seems to define a conservative lower boundary. The situation is not so clear for the embedment strength of oriented strand board (OSB). Test results are very scarce and do not account for the inhomogeneity regarding the thickness of the boards with higher density at the surfaces, which is the section where contact forces are transferred. In the second part, over 110 specimens considering eight different types of nailed connections were tested to assess different calculation procedures. The study focused on nailed connections with OSB and solid timber. This combination together with smooth nails as fasteners is very common in Europe for light-frame structures, especially in areas of low and medium seismicity because they exhibit large deformation capacity without losing strength. On the level of mean values, relationships are found between 1.00 and 1.47 for experimental results over calculated resistance, and it was found that the EYM is more conservative when the thickness of the sheathing is 10 mm instead of 18 mm, which means, that the expected failure mechanism changes from one to two plastic hinges. The findings are approximately the same if the relationship is studied on the level of characteristic values. Here, the relationship of values from experimental investigations over analytical calculation lays between 1.27 and 1.58 for a mechanism with one plastic hinge and between 0.90 and 1.12 for a mechanism with two plastic hinges. Based on these results, the question arises, if the EYM is the appropriate tool to predict the capacity of laterally loaded connections if comparatively large deformations occur between the connected parts. This question should be studied more detailed in the future.

Numerical and Experimental Assessment of an Improved Design Detail for Partially Grouted Reinforced Masonry Wall Structures

AbstractReinforced masonry buildings predominantly are partially grouted in areas of low or moderate seismicity in North America. The walls in such structures typically contain widely spaced separa...

Discrimination between local earthquakes and quarry blasts in the Vértes Mountains, Hungary

We present our analysis of the characteristics of the waveforms of earthquakes and quarry blasts that occurred within extreme local-distance (< 25 km) of Csókakő (CSKK) station in the Vértes Hills, Hungary. Our motivation was to determine the linear discrimination line between the earthquake and explosion populations. CSKK is located in the Mór Graben, a seismically relatively active region, and also characterized by significant mining activity. Contamination of earthquake catalogues with anthropogenic events largely complicates seismotectonic interpretation. It is especially true for relatively low seismicity areas, such as Hungary where more than 50% of the recorded seismicity is attributed to anthropogenic events. We tested the effectiveness of the maximum P/S amplitude ratios in various frequency bands. Because most of the quarry blasts are carried out by ripple-fire technology, we also computed spectrograms and examined the spectral ratio between low and high frequencies and the steepness of spectra. We found that earthquakes and quarry blasts are best separated by the linear discrimination that combines the amplitude ratios and the different spectral ratios.

Parametric study on the I-shape brace connection of conventional concentrically braced frames

Concentrically braced frames (CBFs), designed using the conventional linear elastic method without seismic proportioning and detailing requirements, are referred to as Conventional CBFs (CCBFs) in this study. They are widely used in moderate and low seismic areas in North America due to the ease of design and economy. Without a code specified dedicated fuse member to dissipate earthquake induced energy, or a prescribed yield/failure hierarchy, the brace connection of a CCBF is usually the weakest link in the lateral load-carrying path and prone to fracture. The brace connection is therefore determinant for the structural seismic performance. In this paper, a parametric study based on a validated numerical simulation procedure was carried out on a typical I-shape brace connection, i.e. the flange plate connection. Three key design parameters, namely, the gusset plate thickness, the flange lap plate thickness, and the web lap plate thickness, were varied to study their effects on both the compressive and tensile behaviour of the brace and connection assembly. Various possible failure modes were revealed both in compression and in tension. The results showed that the brace end restraint provided by flange plate connections in CCBFs was significant; the pinned-end assumption would lead to conservative estimation of the brace buckling resistance, which might trigger detrimental gusset plate buckling. The tensile overstrength of the flange lap plate, due to the presence of transverse tensile stress along the net section, was quantified using the von Mises criterion. Design recommendations are proposed with regards to attaining better deformation capacity.