Moderate Seismic Events Research Articles

Observed failure modes in existing URM buildings after November 26, 2019 earthquake in Albania

This study explores the vulnerability of Unreinforced Masonry (URM) structures to seismic events, aiming to uncover the causes of failure and propose reconstruction strategies. Despite often being devastated in powerful earthquakes, URM buildings show damage even in mild to moderate seismic events. Field assessments after a magnitude 6.4 earthquake near Durres, Albania, in 2019, revealed severe damage in masonry buildings and adobe dwellings. Weak structural connections, insufficient roof support, and the absence of bond beams in load-bearing walls were identified as key contributors to the observed damage. The survival of masonry buildings post-earthquake does not guarantee seismic safety. The study recommends reinforcement techniques like shotcrete application, space reduction, and corner reinforcement, along with innovative methods such as Fiber Reinforced Polymer (FRP) use, for existing undamaged unreinforced buildings. These measures aim to prevent damage in the aftermath of destructive earthquakes, offering insights for the resilience of URM structures.

Comparison of earthquake classification systems in local magnitudes ML in some regions of Northern Eurasia

The ML local magnitudes of the earthquakes of Armenia, Azerbaijan, the Arctic and the Baltic Shield (KOGSR and FCIAR station networks), the Urals and Altai and Sayan were analyzed. The regional dependences of ML on the mbISC “external” magnitude are established. It is shown that the magnitudes ML of weak and moderate seismic events registered by the seismic stations of these regions, with the exception of Altai and Sayan, are close at the same mbISC both among themselves and to ML according to the NAO, HEL, DDA, TEH networks of neighboring countries. For all regions, except for Altai and Sayan, a general dependence is established in the form: MLav=1.06⋅mbISC–0.34. A significant overestimation of the ML of Altai and Sayan earthquakes recorded by the regional network is found relative to other data. For the main group of data, the excess of local magnitudes ML=f(KR) over magnitude M in the known T.G. Rautian ratio, KR=lgE=1.8⋅M+4, by DM=0.2÷0.4 in the magnitude range of ML=1.0÷6.0 is shown. For Altai and Sayan earthquakes, the overestimation of local magnitudes is more significant and should be taken into account when calculating seismic energy using the regional ratio KR=f(ML). In general, magnitudes in the ratio KR=1.8⋅M+4 for weak and moderate earthquakes are closer to local magnitudes ML, and for strong events with KR>13 (Ms>5.0) – to surface wave magnitudes Ms.

Seismic risk assessment: the case study of Barberino di Mugello municipality

Recent seismic events, that occurred in the Italian territory, highlighted the importance of increasing knowledge about seismicity and seismic risk. To this aim, in recent years scientific research developed several models for assessing seismic risk and seismic vulnerability of the built environment. In this paper, the seismic risk assessment of the Mugello area is presented, with particular attention to the municipality of Barberino di Mugello within the Florence district. Seismic vulnerability at the territorial scale is assessed by applying and then comparing the results of different literature approaches. Furthermore, the comparison between the results obtained and the observed field data collected from the AeDES forms is proposed in terms of unusable buildings. AeDES forms were filled out by different technicians after the moderate seismic event (Mw 4.5) that struck the Mugello area in December 2019.

Detection of infill wall damage due to earthquakes from vibration data

AbstractVibration‐based methodologies are nowadays gaining increasing application for the structural health monitoring and damage detection on buildings, especially damage due to earthquakes. A fast and efficient damage recognition on structural and non‐structural components can support the decision‐making process after exceptional events and may contribute to reduce troubles due to the inoccupancy of buildings.The paper offers insights on the usefulness of vibration data for the damage detection in infilled frame structures starting from the tracking of the stiffness and modal properties of an infilled laboratory steel‐concrete composite mock‐up subjected to vibration‐based tests. The mock‐up has been object of an extensive experimental campaign that involved both quasi‐static cyclic and dynamic tests characterized by different level of excitation provided to the structure. Cyclic load tests are performed to simulate the effects of earthquakes by progressively increasing the imposed displacement to the cracking and then to the failure of infills. The dynamic tests are executed at the various steps to capture the effects of the infill damage on the global dynamic response triggered by excitations of different amplitudes. Results of dynamic and quasi‐static tests are used to correlate the infill damage with the mechanical properties and the modal parameters of the mock‐up, as well as with the vibration amplitude, providing information about the damage expected during low and moderate seismic events as a function of the registered dynamic response of the building by structural health monitoring systems.

Seismic Performance of a Hybrid Coupled Wall System Using different Coupling Beam Arrangements

This study implemented multirecord nonlinear dynamic and fragility analysis in order to gain more insight into the hybrid coupled wall (HCW) system. Two potentials are used to construct coupling beams, which are the typical steel coupling beam and the replaceable steel coupling beam. Furthermore, an innovative idea for replaceable beams is discussed utilizing reinforced concrete infill instead of steel stiffeners. A new simplified FE model for such beam is carried out in order to explore how this new beam influences the seismic performance of HCW system. An additional equivalent bare RC wall case study is also taken into account for a comprehensive comparison. A precise 2D modelling method using Opensees platform is adopted after validation against experimental and complex 3D numerical simulations. The results indicate a good effect of the replaceable coupling beams concept upon reducing the vulnerability of wall piers under low and moderate events. In terms of coupling beams fragility, the replaceable steel coupling beams also demonstrate better damage resistance when compared with typical steel beams under low and moderate seismic events. Using reinforced concrete infill instead of steel stiffeners can significantly protect beams maintenance without affecting wall piers’ vulnerability.

Characterization of Distant and Moderate Earthquakes with Inexpensive MEMS Sensors: Application to the Mw 6.3, 29th December 2020, Petrinja Event.

In this work, we evaluate the suitability of a new MEMS sensor prototype, called ASX1000 (ADEL s.r.l., Modena, Italy), for the monitoring of distant and moderate seismic events. This device is an inexpensive capacitive accelerometer with a relatively low level of instrumental noise; it can record both local and far seismic events. An experimental network built with ASX1000 MEMS, located in northern Italy, was able to record the Mw 6.3 Petrinja earthquake that occurred in December 2020; it had an epicentral distance of more than 350 km. We retrieved the strong motion parameters (PGA, pseudo-absolute velocity, and pseudo-absolute spectral acceleration) from the acceleration time histories recorded by the MEMS sensors. The obtained parameters were compared with the ones obtained by the closer high-quality seismometers, belonging to the INGV National Seismic Network. The comparison to the highest-quality sensors confirms a reasonable agreement of the inferred parameters. This work suggests that—in the near future—MEMS sensors could be adopted to integrate the existing seismic network. A denser coverage of sensors can sample more accurately the seismic wavefield, taking into account the large spatial variability of local geology and the relative differences in seismic response.

AMBIENT SEISMIC NOISE VARIATIONS BEFORE EARTHQUAKES IN THE BAIKAL RIFT SYSTEM

This paper proposes a method to observe the pre-earthquake features based on the variations in ambient noises using local moderate and strong seismic events as an example. Eight earthquakes in the Baikal rift system with energy classes K=10.1–15.9 were associated to a significant decrease in the level of ambient noises at epicentral distances from 3 to 81 km a few hours before the shock. The observed decrease in the ambient noise level can be classified as a short-term precursor of the medium consolidation 4–5 hours before the earthquake.

Tectonic geomorphology along the transverse basement fault (Moradabad fault) in the Ganga basin: A nexus between the Himalayan tectonics and the pre-Himalayan transverse basement structure

The present study focuses on the neotectonic perspective of a subsurface basement fault, i.e., the Moradabad Fault (MF) in the Ganga basin. This is a ∼163 km long NE-SW trending prominent pre-Himalayan subsurface structure that participated in many phases of tectonic movement during and after the Himalayan orogeny. At present, it is deep-buried under the alluvium, and frequent geomorphic readjustments are seen in the fluvial archives around this fault. The datasets presented here include tectono-geomorphological analysis, transverse-tectonic analysis, previous seismic records from the earthquake catalogs and the associated seismites, and the Ground Penetrating Radar (GPR) studies. The available geological maps limit the northern end of the MF at the Himalayan front, and further northward, it is marked as lineaments. However, the recent geological evidence such as the river alignment, river confluence, landslides, faceted spurs, triangular facets, truncated spurs, fault scarps, structural terraces, and the alignment of the low to moderate magnitude seismic events having parallel trends with the MF may conclude that it is not just a matter of coincidence. However, these features are likely aligned due to the post-Himalayan reactivation-regeneration of the basement structures. It is, therefore, argued that these linear structures showing active deformation are the extension of the MF into the Himalayas, and hence the lineament terminology for these structures should be abolished. The MF has a curved fault-line with the existence of the releasing bend in a transtensional regime. The up-thrown block shows the signs of compression, evidenced by the geomorphological signatures. The fault-bend is characterized by oblique deformation may be accommodated by oblique-slip faulting or dip-slip fault displacements. Tectonic geomorphological characteristics, morphostratigraphic record, GPR data, seismic events, and the basement contour model suggest the Moradabad fault is neotectonically active and is influenced by the Himalayan tectonics.

Out-of-Plane Experimental Study of Strengthening Slender Non-Structural Masonry Walls

Non-structural masonry partition walls, which are mainly designed to functionally separate spaces in the buildings and provide physical barriers between rooms, were traditionally built from either solid or hollow clay units or autoclaved aerated concrete blocks. Recent earthquakes have revealed the high vulnerability of these elements, even in the case of low to moderate seismic events. Public buildings (e.g., hospitals and schools) are particularly vulnerable. Due to their greater floor-to-floor heights and the response spectra of floors, the dynamic response of primary structure may provoke significantly higher seismic loads on partition walls. The main goal of the presented experimental study was to investigate the behavior of slender partition walls loaded out-of-plane with a simple and cost-effective approach that may be applied through routine refurbishment works. Eleven full-scale slender non-structural masonry partition walls were built with brickwork and cement–lime mortar. Eight of them were additionally strengthened with different techniques, including glass fiber-reinforcing fabric and low-cost glass fiber-rendering mesh. To evaluate the efficiency of the applied strengthening solutions, out-of-plane quasi-static cyclic experiments were conducted. By applying meshes over the entire surfaces, the resistance was significantly improved with the low-cost approach reaching half of the resistance of the commercially available strengthening system preserving the same displacement capacity.

Long- and Short-Term Monitoring of a Dam in Response to Seasonal Changes and Ground Motion Loading: The Test Case of the Kurpsai Dam, Western Kyrgyz Republic

An experimental multi-parameter structural monitoring system has been installed on the Kurpsai dam, western Kyrgyz Republic. This system consists of equipment for seismic and strain measurements for making longer- (days, weeks, months) and shorter- (minutes, hours) term observations, dealing with, for example seasonal (longer) effects or the response of the dam to ground motion from noise or seismic events. Fibre-optic strain sensors allow the seasonal and daily opening and closing of the spaces between the dam’s segments to be tracked. For the seismic data, both amplitude (in terms of using differences in amplitudes in the Fourier spectra for mapping the modes of vibration of the dam) and their time–frequency distribution for a set of small to moderate seismic events are investigated and the corresponding phase variabilities (in terms of lagged coherency) are evaluated. Even for moderate levels of seismic-induced ground motion, some influence on the structural response can be detected, which then sees the dam quickly return to its original state. A seasonal component was identified in the strain measurements, while levels of noise arising from the operation of the dam's generators and associated water flow have been provisionally identified.

Minor seismic hazard changes in the broader area of Pournari artificial lake after the first filling (W. Greece)

The broader area of Pournari dam (Western Greece) is investigated regarding the potential seismic hazard change after its impoundment in the early 1980’s. During this impoundment, an increase in local earthquake activity with certain features of induced seismicity was observed. Within the third and fourth month after the first filling, two moderate seismic events occurred, on March 10, 1981 (ML=5.6) and on April 10, 1981 (ML=4.7), with focal depths 13 km and 10 km, respectively, indicating migration of seismicity to shallower depths. The latter is considered as mechanical response change of background from undrained to the drained response (flysch formation).We investigate the potential local seismic hazard and the induced seismicity changes due to the establishment of the reservoir using three time-windows. The first one covers the period up to 1980, before the impoundment, the second starts immediately after the impoundment (1981-2009), while the third is focused on the whole instrumental period 1900-2009. For these time-windows, seismic hazard was initially assessed using the extreme values method. The traditional Cornell-McGuire approach was following applied for the whole instrumental period as a validation test, regarding the reliability of the results obtained by the extreme values method. The results reveal a small decrease of the estimated values of Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV) and maximum expected magnitude (Mmax). The results are compared to the seismic hazard study case of Polyphyto dam (NW Greece), located on a different seismotectonic regime.

Magnetotelluric investigation in the swarm prone intraplate Talala region of Saurashtra, Gujarat, western India

The Talala region of Saurashtra has experienced three moderate seismic events of magnitudes Mw5.0, Mw4.8 (on 6th November 2007), and Mw5.1 (on 20th October 2011) accompanied by swarms. The local earthquake data suggested two epicentral trends (ENE- WSW and NNW-SSE). The focal mechanism of all three earthquakes exhibit strike-slip mechanism with nodal planes sympathetic to these two trends. Based on low gravity values and ambiguous seismic reflections, the ENE-WSW trending fault was inferred and named as Girnar fault. The Magnetotelluric (MT) investigation has been carried out (i) to locate and characterize the Girnar fault and (ii) to ascertain the cause of seismicity in the region. The MT data is acquired along the ~62 km long NW-SE oriented profile, starting from the Sendarda village (NW) to the Hadmatiya village (SE) in the Junagadh district (Saurashtra), India. The regional strike of N19°E is obtained from the MT data. The data is subjected to 2D modeling and two conductors are identified along the profile, the first conductor is located between Ajeb and Aambalgadh village in the northern part of the profile with a resistivity range from 20 to 3500 Ohm.m and the second conductor is ~15 km south of the first conductor near Hirenvel village with a resistivity range from 50 to 3500 Ohm.m. The second conductor continues vertically down to 12–15 km depth and inferred as the Girnar fault. The shallow clustered seismicity (~5 km) near the second conductor advocates that it may be related to stresses induced by intense monsoon on the critically stressed Girnar fault, which has fractured the basement. The basement got fractured either from the local stress accumulation near the structural boundary or from the movement of the fluids to the less permeable crust.

The 13 July 2019 Mw 5.0 Jijel Earthquake, northern Algeria: An indicator of active deformation along the eastern Algerian margin

On July 13, 2019, a moderate earthquake shook the Jijel region of Algeria, ~300 km east of Algiers (Capital of Algeria). In the past, the Jijel region experienced a destructive earthquake (I0: X) on 21–22 August 1856, triggering a moderate tsunami in the western Mediterranean region. The 2019 event is the second important event to have occurred along this part of the Algerian margin, which has been undergoing an inversion process since the Pliocene Epoch. The event occurred 40 km to the north of Jijel City, at 10 km depth. No property damage or injuries were associated with this event. The seismic moment release estimated from waveform modeling was M0 = 3 × 1016 Nm, corresponding to a Mw 5.0 event. The mainshock focal mechanism is associated with the rupture of an E–W thrust fault that is clarified by a 4-km-long × 10-km-wide aftershock cluster along the continental slope of the Jijel margin. In the same area, ~30 km to the west and offshore of the coastal village of Ziama–Mansouriah (west of Jijel) a Mw 4.1 earthquake occurred in 2014. This event is also associated with the rupture of a western contiguous E–W thrust fault. Stress tensor inversion produces a main (σ1) maximum stress axis oriented N356E, which is in agreement with previous stress studies of the Lesser Kabylia–Babors block. The present-day stress field is characterized by a compressional tectonic regime (R' = 2.96 ± 0.21). Coulomb stress analysis of the 2014 Ziama and 2019 Jijel earthquakes indicates that the two earthquakes appear to be individually triggered events with no stress transfer between them. The 2019 Jijel earthquake is associated with one of the three active en echelon faults that have already been identified in the central part of the Algerian margin via recent marine surveys. It belongs to the serie of many moderate seismic events that have recently affected the Algerian margin (Boumerdes, Algiers, Bejaia), and is representative of the active deformation process along the Algerian margin that is marked by the initiation of an incipient subduction zone with a progressive plate boundary migration since the late Miocene.

Effect of prior small to moderate seismic events on monotonic undrained shear strength of sand

In this study we investigate the effect of prior seismic shaking on the monotonic shear strength of saturated Ottawa Sand 20/30. We perform a series of stress-controlled undrained cyclic triaxial tests with different seismic intensities intentionally without causing failure, followed by drainage of the excess pore pressure and an undrained monotonic loading test to determine the undrained shear strength. The experimental data show that small to moderate seismic events that do not fail the specimen can significantly increase undrained shear strength without much change in relative density. One prior seismic event with peak ground acceleration ~ 1.3 m/s2 may increase the undrained shear strength of a specimen at ~ 10 m depth by around 30%. The results also show that as the intensity of the shaking increases, the increase in the monotonic shear strength increases. However, the strengthening effect does not increase with the number of seismic events although a small degree of global densification in the sample is observed. The results of this paper will help assess the change in static slope stability after a single or multiple small to moderate events occurred without causing initial instability.

Are seismic fragility curves fragile?

A hypothetical seismic site is constructed for which the probability law of the seismic ground acceleration process X(t) is specified. Since the seismic hazard is known, the performance of the incremental dynamic analysis- (IDA) and multiple stripe analysis- (MSA) based fragilities, which are used extensively in Earthquake Engineering, can be assessed without ambiguity. It is shown that the IDA- and MSA-based fragilities are unsatisfactory for moderate and large seismic events, are sensitive to the particular parameters used for their construction, and may or may not improve with the sample size. Also, the usefulness of the optimization algorithms for selecting ground motions records is questionable.

Externally bonded carbon fiber–reinforced polymer composites for seismic retrofit of reinforced concrete coupling beams designed according to old codes

A large number of existing buildings have seismic-resistant systems designed according to old code provisions. These structural systems exhibit non-ductile behavior and can present a significant risk in the case of a moderate or significant seismic event. Reinforced concrete–coupled shear walls designed to old codes and standards are among those deficient structures that need to be seismically upgraded. This article aims to investigate a new retrofitting and upgrading method using externally bonded carbon fiber–reinforced polymer composites for existing or/and damaged reinforced concrete coupling beams that can improve the seismic performance of them during earthquakes. To this end, an experimental test was conducted to evaluate the seismic behavior of two identical reinforced concrete–coupled shear wall specimens under reverse cyclic loading. To simulate the old existing building, the specimens were designed and constructed according to the old 1941 National Building Code of Canada with a conventionally reinforced coupling beam. One of the specimens was tested as a control, and the other was strengthened using externally bonded carbon fiber–reinforced polymer composites to evaluate the improvement in its seismic performance. Results show that the retrofit using externally bonded carbon fiber–reinforced polymer resulted in significant enhancement in strength and energy dissipation capacity compared to the conventionally reinforced coupling beam from the control specimen. In addition, externally bonded carbon fiber–reinforced polymer sheets resulted in much improved hysteretic and ductile behavior and in lesser strength and stiffness degradation.

In situ repair technique of infill masonry walls in steel frames damaged after an earthquake

The present paper first reviews the scientific information about masonry buildings in terms of the structural performance of different masonry walls, usual pre-earthquake retrofitting methods, and post-earthquake repair methods. From this, it is found that limited information is available on applicable repair methods for damaged masonry walls after the occurrence of an earthquake event. There is an essential need from the perspective of disaster management strategies to provide urgent aid to casualties of moderate seismic events well before preparing damage assessment data and a comprehensive retrofitting program for the earthquake-affected area. For this reason, three experiments were designed to investigate the effect of brick masonry infill on a simple steel frame and the success rate of a new method of repairing damaged infill. In the proposed repair method, cracks in the damaged masonry infill are stitched by crimped wire meshes in the shape of Band-Aids and cementitious plaster is used to coat the attached wire meshes. The crimped wire meshes must be fastened to the infill with hooked driven nails and must be attached perpendicular to diagonal crack paths and the four corners and centre of the infill. This method is presented for efficient and simple in situ repair interventions to provide temporary residency for casualties. Usage of plasters including accelerated cement or application of accelerated curing methods can reduce the time of repair construction and prepare the proposed method for urgent aids against aftershocks. No inappropriate structural effects of the steel frame-infill interaction were observed during these tests. Furthermore, the results indicated that the repair method not only restored the lost strength of the damaged infill but also recovered the stiffness and ductility of the reference specimen based on the experimental evidence. Following the experiments, a practical design methodology for the required crimped wire mesh specification based on the length of the infill diagonal cracks was recommended.

L’Aquila, central Italy, and the “disaster cycle”, 2009-2017

PurposeThe purpose of this paper is to offer a critical examination of the aftermath of the L’Aquila earthquake of 6 April 2009. It considers the elements of the recovery process that are unique or exceptional and endeavours to explain them.Design/methodology/approachThe analysis is based on a survey and synthesis of the abundant literature on the disaster, coupled with observations from the author’s many visits to L’Aquila and personal involvement in the debates on the questions raised during the aftermath.FindingsSeveral aspects of the disaster are unique. These include the use of large, well-appointed buildings as temporary accommodation and the efforts to use legal processes to obtain justice for alleged mismanagement of both the early emergency situation and faults in the recovery process.Research limitations/implicationsPolitics, history, economics and geography have conspired to make the L’Aquila disaster and its aftermath a multi-layered event that poses considerable challenges of interpretation.Practical implicationsThe L’Aquila case teaches first that moderate seismic events can entail a long and difficult process of recovery if the initial vulnerability is high. Second, for processes of recovery to be rational, they need to be safeguarded against the effects of political expediency and bureaucratic delay.Social implicationsMany survivors of the L’Aquila disaster have been hostages to fortune, victims as much of broader political and socio-economic forces than of the earthquake itself.Originality/valueAlthough there are now many published analyses of the L’Aquila disaster, as the better part of a decade has elapsed since the event, there is value in taking stock and making a critical assessment of developments. The context of this disaster is dynamic and extraordinarily sophisticated, and it provides the key to interpretation of developments that otherwise would probably seem illogical.

North Korea's 2017 Test and its Nontectonic Aftershock

AbstractSeismology illuminates physical processes occurring during underground explosions, not all yet fully understood. The thus‐far strongest North Korean test of 3 September 2017 was followed by a moderate seismic event (mL 4.1) after 8.5 min. Here we provide evidence that this aftershock was a nontectonic event which radiated seismic waves as a buried horizontal closing crack. This vigorous crack closure, occurring shortly after the blast, is studied in the North Korea test site for the first time. The event can be qualitatively explained as rapid destruction of an explosion‐generated cracked rock chimney due to cavity collapse, although other compaction processes cannot be ruled out.

Structural Resistance of Reinforced Concrete Buildings in Areas of Moderate Seismicity and Assessment of Strategies for Structural Improvement

Moderate magnitude seismic events have occurred during the last decade in non-seismic areas and have highlighted that many existing buildings do not sufficiently resist these types of events. The objective of this work is to illustrate that most buildings dating from 2002–2010 constructed from wide beams, which were designed to previous earthquake resistance codes, do not offer a satisfactory seismic behaviour, and to identify which structural attributes can best help alleviate this problem. In this work the effect of a real earthquake of medium magnitude (Lorca, 2011) on buildings of three, five and eight stories with unidirectional frames of wide-beam concrete was assessed. The methodology included non-linear static (pushover) analyses and dynamic response simulations with the aim to understand the effect on the seismic performance of changing some of the geometrical and material parameters. Maximum displacements and capacity curves for the top floor of a set of representative buildings were evaluated and compared. In particular, capacity curves obtained from non-linear static (pushover) analysis are compared for different building configurations, as well as the maximum displacements obtained through non-linear dynamic analysis. This paper highlights the seismic vulnerability of buildings constructed between 2002 and 2010 and the results indicate that a higher density of infill walls (walls whose bricks are not part of the main structure) is the feature that most significantly improves the seismic behaviour of the structures analysed. Moreover, counterintuitively, incorporating stronger concrete and reinforcing steel and using alternative column arrangements only have a small positive effect on the seismic behaviour of these types of buildings.