Regional Seismic Activity Research Articles

Combined bending-torsion and compression-bending-torsion behaviours of reinforced concrete-filled thin-walled corrugated steel tubes

Reinforced concrete-filled thin-walled galvanized corrugated steel tube (RCFCST) is a novel composite member that has application potential in extremely corrosive environments and seismic activity regions. A series of preliminary works have been conducted on its compressive, flexural, shear, and torsional behaviour. However, the combined loading condition is almost inevitable in practice. The correlations between the flexural and torsional behaviour of RCFCSTs are unique due to the special spiral corrugated profile, which is unclear and needs to be addressed. This paper, therefore, presents an experimental investigation of the RCFCST under combined bending-torsion and compression-bending-torsion loads, encompassing the main test variables of torsion-to-bending ratios, torsional directions, and axial compression ratios. The loading set-up and instruments have been introduced in detail. The failure modes, lateral load versus lateral displacement curves, bending moment versus flexural lateral displacement curves, torsion moment versus torsional angle curves, and strain distributions are carefully addressed. The working mechanisms of the RCFCST under monotonic combined loads are discussed, with a particular explanation of the dependent behaviour on the torsion-to-bending ratios and torsional directions. The applicability of the existing design methods for the bearing capacity of RCFCST specimens under combined loads is examined carefully, with specific design suggestions proposed.

Cyclic behavior of cold-formed stainless steel sandwich tubular brace: An experimental investigation

Stainless steel shows promise for application in seismic-active regions. Previous research showed that stainless steel dampers could exhibit good energy dissipation capacity and high post-yield stiffness under cyclic loading. In light of that, a novel type of cold-formed stainless steel sandwich tubular brace (STB) is presented in this study, featuring one stainless steel square hollow section (SHS) tube as the load-carrying component and two additional stainless steel SHS tubes providing a buckling-restraining effect. Six specimens were tested under cyclic loading, varying parameters including the cross-section slenderness of the core tube, restraining ratio and loading histories. Loading protocols encompassed standardized ones following the Chinese specification (CN) and American provision (US), as well as a protocol representing the near-fault earthquakes (NF). Failure modes, hysteretic response and seismic performance indexes were obtained. Results showed that the hysteretic curves could maintain stable. Under the CN loading protocol, the specimen with a slender core cross-section exhibited uniform local buckling. The strain hardening coefficient ω stayed within the range of 1.46–1.58. The specimens exhibited a slow decay rate of tangent stiffness, highlighting their relatively high post-yield stiffness. The cumulative energy dissipation factor could reach 658, signifying good energy dissipation capacity. Additionally, under NF loading, specimens exhibited enhanced cumulative ductility compared to CN or US loading. Furthermore, an evaluation was conducted to assess the suitability of existing design methods for preventing overall buckling and local bulging in stainless steel STBs. It indicated that the current design approaches tended to be overly conservative for both overall and local stability design of stainless steel STBs, primarily due to the lack of consideration for SHS core stiffness and the interactions between flanges and webs, respectively.

Three-dimensional path-effect model to simulate ground motion attenuation on the Korean Peninsula

In low-to-moderately active seismic regions such as the Korean Peninsula, it is difficult to analyze seismic hazards because only a limited number of strong ground motions have been recorded. To address this shortcoming in the data, ground motion simulation can be used to generate the strong ground motions associated with potentially large earthquakes, taking into account the attenuation that occurs as the distance from the source increases. To simulate this attenuation, the path effect, which is a component of the Fourier amplitude spectrum ( FAS), needs to be defined, along with the source and site effects. The path effect represents the propagation of seismic rays through a tectonic medium. In this study, a three-dimensional (3D) path effect model is developed for the Korean Peninsula, consisting of a 3D geometrical spreading factor, quality factor, and shear-wave velocity. The accuracy of the proposed model is verified by comparing the path-effect values obtained from the FAS of individual ground motions recorded on the Korean Peninsula and those calculated from the model. Examples that demonstrate the procedure to calculate the 3D path effect for the Korean Peninsula are also provided.

Investigation of the dynamic response of h-type anti-slide pile based on shaking table test

The h-type anti-slide piles (hTPs) are extensively utilized in slope stabilization projects, yet their response to seismic activities remains inadequately understood. This study investigated the dynamic response of hTPs with circular cross-sections (hTCPs) through a shaking table test, focusing on seismic events along Jiuzhaigou-Mianyang highway slopes (ZK142 + 124 to ZK142 + 274). Time-frequency analysis using Fast Fourier Transform (FFT) and Hilbert-Huang Transform (HHT) was conducted. The peak acceleration and its direction, dynamic earth pressure and its sharing ratio, and moment were characterized, and the variations of pile displacement and the seismic damage on different parts of hTCPs were analyzed under varying loading conditions. Results reveal a distinct pressure distribution and damage characteristics between the long and short piles in hTCPs. A positive correlation between peak accelerations and loading conditions was observed in both long and short piles, with peak amplification occurring only at the top of long piles. Long piles exhibited diverse acceleration directions under different loading conditions, contrasting with the infrequent occurrence in short piles. The peak dynamic earth pressure distribution varied between the front and back side of pile bodies, with opposite overall trends between the long and short piles. The sharing ratio displayed an increasing followed by decreasing trend in long piles, but an opposite trend in short piles, with the turn point occurring at a loading condition of 0.3 g. These differences were significantly influenced by El Centro waves within a low frequency band (13.34 Hz–16.18 Hz), as a single large peak HHT energy spectrum was observed in long piles, but multiple and destructive low-frequency energy spectra in short piles. The results suggest an independent dynamic response occurred in the long and short piles of hTCPs during shaking table test, providing insights for their field engineering application in seismic active regions.

Reconnaissance of the Effects of the MW5.7 (ML6.4) Jajarkot Nepal Earthquake of 3 November 2023, Post-Earthquake Responses, and Associated Lessons to Be Learned

On 3 November 2023, a moment magnitude (MW) 5.7 (Local Magnitude, ML6.4) earthquake struck the western region of Nepal, one of the most powerful seismic events since 1505 in the region. Even though the earthquake was of moderate magnitude, it caused significant damage to several masonry buildings and caused slope failures in some regions. The field reconnaissance carried out on 6–9 November by the study team, following the earthquake, conducted the first-hand preliminary damage assessment in the three most affected districts—Jajarkot; West Rukum; and Salyan. This study covers the observed typical structural failures and geotechnical case studies from the field study. To have a robust background understanding, this paper examines the seismotectonic setting and regional seismic activity in the region. The observations of earthquake damage suggest that most of the affected buildings were made of stone or brick masonry without seismic consideration, while most of the reinforced concrete (RC) buildings remained intact. Case histories of damaged buildings, the patterns, and the failure mechanisms are discussed briefly in this paper. Significant damage to Khalanga Durbar, a historical monument in Jajarkot, was also observed. Medium- to large-scale landslides and rockfalls were recorded along the highway. The motorable bridge in the Bheri River suffered from broken bolts, rotational movement at the expansion joint, and damage to the stoppers. The damage observations suggest that, despite the existence of building codes, their non-implementation could have contributed to the heavy impact in the region. This study highlights that the local population faces a potential threat of subsequent disasters arising from earthquakes and earthquake-induced landslides. This underscores the necessity for proactive measures in preparedness for future disasters.

Analysis of space images of the fault system of the Altai-Sayan seismic active region based on Shearlet transform

The paper proposes a method for processing and analyzing satellite images of a territory with increased seismic activity to identify geological inhomogeneities (geological faults, blocks) on the Earth’s surface. The methodology is based on adapted algorithms for discrete Shearlet transform (Shearlet toolbox and FFST). The problems of noise filtering and contour extraction with contrasting and color coding for the studied visual observational data are solved.

Radiological risk estimation from the terrestrial gamma dose rate in the seismically active Kopili Fault Zone, India

ABSTRACT Anomalies in terrestrial gamma radiation have been reported in regions of seismic activity. The Kopili Fault in India is well-known for being extremely seismically active. Several mild to moderate-magnitude earthquakes with epicentres along the Kopili Fault Zone have recently been recorded. This necessitates a measurement of variations in gamma radiation and its associated radiological risks to the population in the region in relation to seismic activities. In this work, a portable gamma survey metre was used to measure terrestrial gamma radiations in the earthquake-prone Dhekiajuli area of Sonitpur district, India, which is located in the Kopili Fault Zone. Indoor and outdoor gamma dose rates were found to be 99.4 ± 5.1–195.9 ± 5.1 nGy h−1 (geometric mean: 159.0 ± 8.8 nGy h−1) and 99.4 ± 5.1–198.8 ± 5.1 nGy h−1 (geometric mean: 132 ± 6.5 nGy h−1), respectively. The estimated total annual effective dose equivalents (geometric mean: 0.94 ± 0.05 mSv y−1) were found to be higher than the recommended global average of 0.48 mSv y−1. The excess lifetime cancer risk was also estimated by considering the life span of an individual as 70 years, which ranged from 2.4 × 10−3 to 4.8 × 10−3.

Regional Multifractal Variability of the Overall Seismic Activity in Pakistan from 1820 to 2020 via the Application of MDFA on Earthquake Catalogs

The overall seismicity of Pakistan from 1820 to 2020 is analysed in terms of its multifractal behaviour. Seismic events of magnitude ML = 3.0 and above are spatially clustered into four distinct groups, each one corresponding to a different region of high seismic activity. The Multifractal Detrended Fluctuation Analysis (MFDA) method applied on each cluster reveals pronounced inter-cluster heterogeneity in terms of the resulting generalised Hurst exponent and fractality spectrum, possibly due to the particular tectonic characteristics of the regions under investigation. Additional results on the variability of the Gutenberg–Richter b-value across the defined clusters further corroborate the uniqueness of the seismic profile of each region.

New paleoseismic events reveal decamillenial recurrence time for large earthquakes (M ≥ 7) along the Yuguang Graben Fault in North China

Paleoseismic studies are critical for the assessment and prediction of large earthquakes (M ≥ 7). These studies involve excavating and analyzing evidence from surface–rupturing earthquakes. However, they often face limitations in spatiotemporal resolution. The Yuguang Graben, located in the northern Shanxi Grabens of North China, contains an abundance of Quaternary loess that can be utilized for extending paleoseismic records. Fine-grained deposits of loess contrast sharply with gravel deposits of the colluvial wedge, making the wedge shape apparent. To enhance our understanding of earthquake behavior in the Yuguang Graben, we excavated a trench on terrace T2 of the Songzhikou segment of the Yuguang Graben Fault (YGF). We used LiDAR to obtain a high–resolution orthophoto of the trench wall. Through OSL dating of colluvial wedges and loess, we identified at least four large paleoseismic events with a magnitude of M ≥ 7 that occurred along the YGF. These events took place at >77.6 ± 5.1, 63.9 ± 5.1, 51.0 ± 4.3, and 37.3 ± 0.3 kyr, respectively. Combined with previous paleoseismic studies, we identified seven paleoseismic events since the late Pleistocene. These findings reveal that earthquakes occurring on YGF follow a quasiperiodic pattern with an average recurrence interval of about 12 ± 3 kyr. The elapsed time of the most recent earthquake near the recurrence interval suggests an increased risk of a large earthquake along the YGF. We also analyzed earthquake clusters generated by neighboring faults in the active northeastern boundary of the Ordos block. Our analysis indicated that fault interactions can affect the recurrence interval of earthquakes along single faults, while regional seismic activity tends to concentrate in time during a seismically active period. These observations underscore the importance of expanding paleoseismic records and exploring regional seismic hazards to gain a more comprehensive understanding of earthquakes.

Seismic hazard assessment studies based on developed deterministic and probabilistic approaches for the central-east of Iran region

PurposeThis Study aims to present the seismic hazard assessment of the earthquake-prone eastern of Iran that has become more important due to its growing economic importance. Many cities in this region have experienced life and financial losses due to major earthquakes in recent years. Thus, in this study the seismic hazard maps and curves, and site-specific spectrums were obtained by using probabilistic approaches for the region.Design/methodology/approachThe seismotectonic information, seismicity data and earthquake catalogues were gathered, main active seismic sources were identified and seismic zones were considered to cover the potential active seismic regions. The seismic model based on logic tree method used two seismic source models, two declustered catalogues, three choices for earthquake recurrence parameters and maximum considered earthquakes and four ground motion predicting (attenuation) models (GMPE).FindingsThe results showed a wide range of seismic hazards levels in the study region. The peak ground acceleration (PGAs) for 475 years returns period ranges between 0.1 g in the north-west part of the region with low seismic activity, to 0.52 g in the south-west part with high levels of seismicity. The PGAs for a 2,475-year period, also ranged from 0.12 to 0.80 g for the same regions. The computed hazard results were compared to the acceptable level of seismic hazard in the region based on Iran seismic code.Originality/valueA new probabilistic approach has been developed for obtaining seismic hazard maps and curves; these results would help engineers in design of earthquake-resistant structures.

Tunnel Stability Analysis Under Seismic Load Using Finite Element Method: A Case Study of Spillway Tunnel, Sidan Dam, Bali, Indonesia

The location of the Sidan Spillway Tunnel, as shown on the Earthquake Hazard Zone Map of Bali Island, is in a moderate hazard zone. The support system of the spillway tunnel of the Sidan Dam, Indonesia, was empirically designed based on rock mass classification systems. The objective of this research was to verify the performance of the proposed support system by a numerical method considering the uncertainty in using rock mass classification systems for designing a tunnel support system. In addition, being located in an active seismic region, the seismic load was not considered in the empirical tunnel support design. The proposed tunnel support design was numerically modeled in two dimensions using a finite element method and subjected to a seismic load obtained from probabilistic seismic hazard analysis. A numerical analysis without seismic load was also conducted for comparison. Phase2 software was used for the tunnel stability analysis. The input parameters in the numerical analysis were derived from field investigations (surface engineering geological mapping and evaluation of drilling cores) and laboratory tests. The spillway tunnel area consists of pyroclastic rocks, and the Generalized Hoek-Brown Failure Criterion was selected for the strength parameter of rocks. The suggested support designs are systematic rock bolts (20 mm diameter fully grouted), wired mesh, shotcrete, and steel ribs at specific locations. The numerical models determined that applying the proposed tunnel support system recommended based on the empirical method resulted in a roof strength factor of more than 1.5 under static load & 1.1 under seismic load and roof displacements lower than a 10 cm maximum displacement at every stage of construction. The results verify that the tunnel construction will be stable and fulfill the required safety standard, both under and without seismic loads.

Regional seismic stratigraphic framework and depositional history of the post-Valanginian passive margin sequences in the Northern Carnarvon Basin, North West Shelf of Australia

The post-rift succession of the Northern Carnarvon Basin (north-western Australia) has commonly been interpreted as a relatively simple and uniform sequence that records a transition from siliciclastic to carbonate sedimentation deposited on a passive margin. However, given the significant vertical and lateral variation in seismic facies visible on seismic data, this interpretation likely oversimplifies the depositional history of the margin. Regional composite seismic lines that cross most of the basin, integrated with lithological and biostratigraphic information from exploration wells, provide the context for a better understanding of the depositional processes and environments that characterize the post-rift continental margin succession. We show that the sedimentary sequences deposited above the Valanginian breakup unconformity contain a wide variety of seismic facies that can be linked to a number of different marine depositional environments, with the greatest lateral variation occurring in the Turonian – Rupelian and in the Tortonian – Present. The former interval consists of three dominant seismic facies, namely polygonally faulted, incised, and parallel bedded, which we interpret to indicate a lateral transition from an environment primarily dominated by fine-grained pelagic/hemipelagic deposition to one dominated by energetic bottom currents that created both depositional and erosional features, such as contourite drifts and associated moats. The latter interval is expressed by sigmoidal and continuous reflections which pass laterally into more chaotic reflection packages, which we interpret as clinoforms and mass-transport complexes (MTCs). The development of bottom currents may be connected to changes in circulation associated with the opening of oceans adjacent to the northwest margin of Australia, while the MTCs may indicate increased regional seismic activity and slope instability resulting from the development of collisional plate boundaries. Definition of these sequences highlights the significant changes that have occurred in the sedimentary processes that operated on the margin, and their potential link to its tectonic evolution.

The relation of regional earthquakes to an intraplate volcano in the northern Hainan Island, China from magnetotelluric imaging

Volcanic activity can cause regional earthquakes before or during an eruption, while violent earthquakes are capable of changing static and dynamic stress-fields that may consequently accelerate or trigger volcanic eruption. It is thus important to consider the volcano and regional earthquake as an integrated system, which has implications for disaster prevention and may enable early warning. In this work, two magnetotelluric (MT) profiles were deployed across the active volcanic and seismic region in the northern Hainan Island, China. Data were inverted to generate a three-dimensional resistivity structure beneath the two profiles. The resistivity model shows a shallow (< 5 km) low-resistivity (< 10 Ωm) zone corresponding to Paleogene and Neogene sediments, and two conductors (10–30 Ωm) at depths of 5–12 km. The conductors in the middle-upper crust are attributed to the accumulation of high-salinity fluids supplied by deeper magmas. The north-south trending small earthquakes (< M3) are mainly distributed in high-resistivity basement, independent of the volcanic plumbing system, which are attributed to small-scale rupture in higher tensile rocks. The volcanic plumbing system appears to extend below the Qiongzhou Earthquake (M7.5 in 1605), indicating the possibility of distal volcano-tectonic earthquake.

Analysis of the Epicenter Location Accuracy for the Local Seismic Network Operated in the Mining Area Towards the Automation of Location Procedures

Legnica-Głogów Copper District (LGCD) is one of the most active seismic regions in Europe. Several thousand seismic events induced by underground copper mines are recorded there each year, with the strongest reaching magnitudes above 4. Seismicity in LGCD is monitored by the LUMINEOS surface seismic network and the mine's underground networks. While the horizontal location uncertainty of the LUMINEOS network is about 300–600 m, the declared epicenter uncertainty of dense mine networks is less than 50 m. It gives us a unique opportunity to test the location accuracy of seismic events recorded by the LUMINEOS network determined with various algorithms and automatic procedure. In our work, we compared the location accuracies of traveltime-based algorithms LocSAT and NonLinLoc as well as waveform-based algorithm BackTrackBB. The iterative, Geiger-type LocSAT algorithm is used in routine daily processing for the LUMINEOS. Its downside is the need to use the S wave onset times, which in the case of the LUMINEOS network are very uncertain. As an alternative, we tested the probabilistic NonLinLoc algorithm, and the waveform based BackTrackBB algorithm. The BackTrackBB algorithm is known to work well with local, high noise seismic networks. We aimed to find out if it could be used routinely with the LUMINEOS data. In addition, we conducted a comparative analysis of the location uncertainty of these algorithms to determine the effectiveness of this parameter in assessing accuracy.

Seismic analysis of a monopile-supported offshore wind turbine considering the effect of scour-hole dimensions: Insights from centrifuge testing and numerical modelling

Monopile-supported offshore wind turbines (OWTs) deployed in seismic-active regions are inevitably threatened by the combined effect of earthquake and scour. However, current codes and research fail to adequately address the seismic response of OWTs under different scour conditions. In this study, a series of centrifuge shaking table tests were conducted on a monopile-supported OWT model subjected to both local scour and general scour. The test results show that the amplification effect of general scour site is more pronounced than that of local scour site. Moreover, the maximum bending moment from the general scour cases are mostly larger than those from the local scour cases under relatively large scour depth. This indicates the possibility of an over-conservative design when simply reducing the local scour condition to general scour condition. Then, based on the centrifuge tests, a practical 2D finite element model is proposed, in which not only the inertial and kinematic effects but also the effect of scour-hole dimensions on the ground motion input pattern and the vertical effective stress along the pile are incorporated. Further parametric study shows that the kinematic effect plays a significant role in the pile response and cannot be simply neglected even under scoured conditions.

Exploratory Data Analysis of Earthquake Moment Tensor Catalog in Japan Using Non-linear Graph-Based Dimensionality Reduction

The catalog of moment tensor solutions, which contains the information on spatial location, origin time and fault mechanism type of earthquakes, has been interpreted by researchers based on a wealth of past knowledge. However, the long-term routine analyses have led to the accumulation of a huge amount of data in the moment tensor catalog, and it is worth considering moving away from the artisanal approach. In this study, using dimensionality reduction of unsupervised machine learning, we performed exploratory data analysis of the moment tensor catalog in Japan to objectively obtain comprehensive images of seismic activity and to acquire knowledge on the spatial and temporal characteristics of the earthquake mechanism. Source parameters of the moment tensor catalog in Japan, spatial location (latitude, longitude, and focal depth) and source-mechanism diagram information were embedded in two-dimensional space via a non-linear graph-based dimensionality-reduction method, Uniform Manifold Approximation and Projection. On the embedding map, earthquakes in eastern and western Japan are distributed separately and are further embedded to reflect their characteristic fault mechanism and focal depth in each region. The similarity degree of the earthquakes can be obtained as the distance on the embedding map. This study demonstrates that the data visualization using dimensionality reduction is useful for intuitively and objectively understanding the regional characteristics of earthquake mechanisms. The embedding map can also be employed to visualize temporal changes in regional seismic activity and to perform a similarity search with a past event.

Reinforcement Related for Construction in Seismic Active Regions. Aspects of Production, Application and Control

Reinforcement Related for Construction in Seismic Active Regions. Aspects of Production, Application and Control

Ocean Bottom Seismometers in Suruga Bay reveal a shear zone inside the Philippine Sea plate slab

Suruga Bay lies along the Tokai segment of the Nankai-trough, which last ruptured in the 1854 M8.4 Ansei-Tokai Earthquake, making it a potential locus for the next major earthquake on the Nankai-trough. Moderate size earthquakes have occurred in the Suruga Trough axial region (M6.5 in 2009 and M6.2 in 2011) that resulted in a prominent excitation of seismicity. Unfortunately, our ability to accurately locate these events is hampered by a sparse routine seismic observation network around the bay. In order to improve location accuracy, a total of 2 sets of 7 OBSs were deployed inside Suruga Bay, 6 from the spring of 2017, and an additional OBS from spring 2019. By combining the data from our OBS stations with that of existing land-based stations surrounding Suruga Bay, we were able to accurately relocate the observed seismic activity inside the Philippine Sea plate (PHS). Our combined processing revealed a 25° northwest-dipping 2–5 km wide zone on which the regional seismic activity occurs. Overall, seismic activity is observed to be 5–10 km shallower than previously determined from routine network data alone. A striking feature of the analyzed activity is the presence of a prominent strike-slip component in the focal mechanisms, which exhibit P-axes almost exclusively oriented towards the north. Furthermore, taking into consideration the apparent difference in the direction of the P-axis of the stress field to the calculated sense of movement of Izu peninsula by GNSS data, and the ongoing internal deformation observed by geodetic and geological data, we propose the existence of a shear zone inside the subducting PHS starting from the southern tip of Izu Peninsula and extending across the bay under Shizuoka city. This zone of strain partitioning acts as a buffer between the northward-colliding Izu Peninsula and the northwest-directed subduction of the PHS observed by GNSS.

Pre-quake frequency characteristics of Ms ≥7.0 earthquakes in mainland China

In this study, natural orthogonal expansion was performed on earthquake frequencies to compute the pre-quake frequency fields of 9 Ms ≥7.0 earthquakes in mainland China from 1980 to 2020. The temporal and spatial pre-quake anomalies of these earthquakes were extracted from their frequency fields. We found that the majority of pre-quake temporal anomalies (i.e., variations exceeding two-times the absolute mean square error) of a strong earthquake are condensed within the first four frequency fields, and typically comprise multiple components. The temporal factor of the first frequency field usually accounts for the largest proportion of these anomalies (40%–60% of the entire field). Most Ms ≥7.0 earthquakes exhibited long-term anomalies 5–8 years before their occurrence; some presented medium-term anomalies 1–2 years prior to the quake, and only a few presented short-term and imminent anomalies (≤3 months before the quake). Anomalous seismic hazard zones have high-gradient turning points in regional frequency-field contour maps, and the epicenters of strong earthquakes are often located in areas containing active faults that have contour values. Through the comparison of seismic frequency field and the traditional method of regional seismic activity frequency (3 months), it is shown that the frequency-field time factor has the advantages of diversified and rich abnormal information. The slope comparison between the frequency field and the cumulative frequency curve shows that the frequency anomaly time of the two is consistent, and the conclusion is reliable. Therefore, the seismic frequency method can predict the occurrence time and location of strong earthquakes, which is closer to the predictable seismic model.

Non-linear Dynamic Analysis of RC Structures Under Earthquake Sequences

Earthquakes in active seismic regions usually occur in a series of medium to strong intensity ground motions at small intervals of times. A large intensity mainshock (MS) is often followed by a series of aftershocks (AS) or even preceded by smaller foreshocks. This sequence type of mainshock-aftershock (MS-AS) ground motions with varying intensity pose major seismic hazard as there is limited scope of repair and retrofitting between seismic events. Due to continuous and repeated seismic ground motions over a brief period of time, the damages in the structure gets accumulated and structure collapse. This study navigates the behaviour of reinforced concrete structures under such seismic sequences. For this purpose, the nonlinear response of three 12 storey reinforced concrete buildings (regular plan, mass irregularity and diaphragm irregularity) is evaluated. The buildings are subjected to five real seismic sequences from previous earthquakes. Nonlinear dynamic analyses are carried out to study the response of buildings under MS and MS-AS sequences considering: a) material and geometric non linearities and b) irregularities. A single highest aftershock is considered in the present study. The results in this study indicates that MS-AS seismic sequence considering both material and geometric nonlinearities has significant effect on the response of structure. It also showed that seismic sequences significantly alter the response of irregular structure.