Mainshock Aftershock Research Articles

Tests of Remote Dynamic Aftershock Triggering by Small Mainshocks Using Taiwan’s Earthquake Catalog

Abstract To understand earthquake interaction and forecast time-dependent seismic hazard, it is essential to determine which static or dynamic stress change due to a mainshock plays a major role in triggering its aftershocks and subsequent mainshocks. Using small mainshocks (2≤M<3) and their aftershocks, Felzer and Brodsky (2006) argued that mainshock induced dynamic stress change is responsible for earthquake triggering in a form of power-law decay within 50 km. Richards-Dinger et al. (2010), however, studied the foreshock decay and claimed that mainshock had no effect at distances outside its static stress triggering range, which required an alternative explanation. We tested these hypotheses using Taiwan’s earthquake catalog by taking advantage of its lack of large events and the absence of active volcano and associated significant seismic swarm. In examining earthquakes occurring in 1994–2010, following Felzer and Brodsky’s method, we found a linear aftershock density with a power-law decay of −1.12±0.38 that is very similar to the one seen in Felzer and Brodsky (2006). None of the mainshock–aftershock pairs were associated with an M 7 rupture event or M 6 event. We further demonstrated that the density decay in a short time period is more likely a randomized behavior than mainshock–aftershock triggering. These pairs were located mostly in high geothermal gradient areas, which are probably triggered by a small-scale aseismic process.

Collapse Capacity of Ordinary RC Moment Frames Considering Mainshock-Aftershock Effects

ABSTRACT The effect of mainshock-aftershock (MS-AS) sequences on seismic performance of ordinary reinforced concrete (RC) moment frames (ORCFs) is studied by considering various levels of mainshock damage represented by maximum inter-story drift (MID) parameter. Incremental dynamic analysis (IDA) is performed to extract collapse capacity of structures under aftershock records after imposing the intended mainshock damage. The study results indicate that a smooth reduction in aftershock collapse capacity occurs due to increase in mainshock damage level. Regression equations are also provided to aid in predicting the aftershock collapse capacity in presence of various mainshock damage levels.

Study of Materials Behavior in a Monumental Vault Strengthened by a Carbon Net in a Mineral Matrix Subjected to Seismic Influence

The application of the elasto-plastic material model known as the Barcelona Model (BM) for numerical assessment of a historical vault subjected to earthquake sequence is presented in this work. As a case study, part of a masonry vault erected in Southern Poland in the 12th century was chosen. For the study purposes, a 3D finite element model (FEM) of the vault was prepared using the ABAQUS/Standard software program. The essential details of the structure geometry were taken from the 3D scan of the vault. The first variant of the masonry vault was the structure without any strengthening, whereas the second variant was with strengthening system realized by application on composite materials, i.e., the carbon fiber reinforced cementitious matrix (C-FRCM). The results of the dynamic analysis revealed that an evident nonlinear performance of the masonry materials of the vault in both cases was detected for both FE models of the structure. The analysis proved that the foreshock–mainshock–aftershock sequence caused substantial damages in structural parts of the masonry vault. The distribution of plastic strains and damages allowed assessment of the impact of the full seismic sequence on the masonry vault. In the case of the unstrengthen vault the level of cracking and stiffness loss reached 90%. In the case of the vault strengthened with the FRCM system the tensile damage level was significantly lower. It did not exceed 30%. In addition, the first plastic zone of the unstrengthened masonry structural elements of the vault became visible after the foreshock.

Time-dependent and spatiotemporal statistical analysis of intraplate anomalous seismicity: Sarria-Triacastela-Becerreá (NW Iberian Peninsula, Spain)

SUMMARY The Sarria-Triacastela-Becerreá seismicity is located in an intraplate region considered seismically stable, but in 1995 started an unprecedented earthquake activity in the area. Since then an anomalous long-term continuous seismicity remains until now in the same location. Despite the long-term seismicity and the large magnitudes for the region standards (5.1 Mw), the origin and mechanisms of this seismicity remains unclear. The isolation of background from the main shock–aftershock contribution by means of the application of the Epidemic Type Aftershock Sequences (ETAS) model, the spatial depiction and the resemblance to near seismic regions allow us to identify several seismicity behaviours. From 1995 to 1998/99, the seismicity in this location mainly consists of intensive and deeper earthquake sequences linked to the 1995 and 1997 main shocks. Our results suggest that the main shocks triggered aftershocks and additionally initiated or facilitated aseismic processes. A likely scenario is that the main shocks broke a sealed source at depth allowing a subsequent intrusion of high-pressurized fluids from depth. The resemblance of this period with Zamora seismic characteristics proposes that Triacastela seismicity was also initiated by tectonic activity. From 1998/99 to 2018, a change in seismicity is observed, the background contribution took control and swarm-type activity is predominant. While the earthquake rate decreases, the relative background contribution goes up. Actually, after 2013 the clusters almost disappear and background contribution achieves 55 per cent of the total activity. The spatial migration to the southeast and the upward trend to shallower depth support fluid migration as possible driving mechanism responsible for the transient seismicity in this period. The swarm-type activity in Triacastela in later periods and the resemblance of b-values with Ponte Caldelas and Ventaniella seismicity suggest that the seismicity in Triacastela is related to fluid migration and the reactivation of fractured areas. We propose that the mechanism of this anomalous and long-term seismicity in Triacastela is the mix of different mechanisms, starting with the tectonic seismicity, generated during the 1995 and 1997 seismic sequences, which initiated a fluid upward migration through fractured crustal fault patches, observed after 1998–1999, and responsible for the seismicity during the following 20 yr.

Evaluation of seismic performance of steel frames with stiffness irregularity subjected to mainshock–aftershock using equivalent single-degree-of-freedom system

Many buildings in the present-day scenario have irregularities due to the discontinuity of their mass, stiffness, and geometry through their height. Buildings with vertical irregularities suffer severe damage as observed in past records. Structures situated in earthquake-prone regions are subjected to multiple earthquakes, occurring at a short interval of time, due to the mainshock–aftershock (MS–AS) sequence. This study investigates the effects of stiffness irregularities on the seismic performance of the 9-storey steel moment-resisting frame (SMRF) subjected to mainshocks and MS–AS. Nonlinear time-history analysis (NTHA) was conducted to compare the height-wise variation of maximum inter-storey drift ratio (IDR) demands of the regular and stiffness irregular frames. The results show that stiffness irregularity through the height of the frame influences the height-wise variation of inter-storey drift. Also, the structural responses of regular and irregular frames subjected to MS–AS are increased compared to mainshocks. This study also evaluates the accuracy of previously proposed three different equivalent single-degree-of-freedom systems (ESDOF) for obtaining seismic demands of multi-degree-of-freedom (MDOF) systems of regular and irregular frames subjected to mainshocks and MS–AS. The mean values of the height-wise variation of IDR obtained from MDOF and ESDOF systems are compared. The effectiveness of ESDOF systems for estimation of IDR is examined by mean bias and standard deviation of the ratio of mean values of IDR determined by NTHA of MDOF systems to the values determined by ESDOF systems. The study concludes ESDOF systems are useful for estimating the height-wise variation of IDR for regular and stiffness irregular frames subjected to mainshocks and MS–AS.

Parametric and non-parametric estimation of extreme earthquake event: the joint tail inference for mainshocks and aftershocks

In an earthquake event, the combination of a strong mainshock and damaging aftershocks is often the cause of severe structural damages and/or high death tolls. The objective of this paper is to provide estimation for the probability of such extreme events where the mainshock and the largest aftershocks exceed certain thresholds. Two approaches are illustrated and compared – a parametric approach based on previously observed stochastic laws in earthquake data, and a non-parametric approach based on bivariate extreme value theory. We analyze the earthquake data from the North Anatolian Fault Zone (NAFZ) in Turkey during 1965–2018 and show that the two approaches provide unifying results.

Seismicity clusters in Central Chile: investigating the role of repeating earthquakes and swarms in a subduction region

SUMMARYSeismicity along subduction interfaces is usually dominated by large main-shock–aftershock sequences indicative of a continuum distribution of highly coupled large asperities. In the past decades, however, the increased resolution of seismic catalogues at some subduction zone seems to indicate instead a more complex rheological segmentation of the interface. Large and megathrust earthquake ruptures seem interspersed among regions of low seismic coupling and less stress buildup. In this weaker zone, the strain is primarily released via a combination of moderate-size swarm-like seismicity and aseismic slip. Along the Chilean subduction zone, the densification of the seismic network allowed for the identification of localized seismic clusters, some of them appearing in the form of swarms before megathrust earthquakes. The origin and driving processes of this seismic activity have not yet been identified. In this study, we follow a systematic approach to characterize the seismicity at two persistent clusters in Central Chile, one located offshore Navidad and one inland, at ∼40 km depth beneath Vichuquén, which occurred throughout ∼20 yr. We investigated these clusters, by deriving high-resolution hypocentral locations and moment tensors and performing a detailed analysis of spatio-temporal patterns, magnitude and interevent time distributions of the clustered earthquakes. Both clusters are characterized by weak to moderate seismicity (below Mw 6) and stand out as clear seismicity rate and Benioff strain anomalies. At the Navidad cluster, seismicity occurs in the form of swarms, with a characteristic duration of 2–7 d and location and thrust mechanisms compatible with activity on the slab interface. Conversely, we find at Vichuquén activity dominated by thrust earthquakes occurring as repeaters on the slab interface, with a slip rate of approximately ∼5.0 cm yr−1. We attribute these clusters to local features of the subducting plate: the Navidad swarms are likely driven by repeated high pore pressure transients along a pre-fractured patch of the slab, while the seismicity at the Vichuquén cluster is interpreted as the result of a subducting seamount. Both clusters have been active before and after the Mw 8.8 Maule earthquake and persisted afterwards with the seismicity decay following the Omori law. These interactions are especially evident for the Vichuquén cluster, where the seismicity rate increased considerably after the Maule earthquake and continues to be an area of clearly elevated seismicity rate compared to its surroundings.

Hysteretic energy‐based state‐dependent fragility for ground‐motion sequences

AbstractA framework to derive state‐dependent fragility relationships of structures subjected to ground‐motion sequences (e.g. mainshock‐aftershock (MS‐AS) or triggered earthquakes) is proposed. The hysteretic energy dissipated in the sequence is adopted as the main demand parameter, as it is a cumulative measure monotonically increasing with the length of the excitation. For a structure subjected to earthquake‐induced ground motions, it is not possible to define a closed‐form representation of the hysteretic energy as a function of the peak deformation. However, based on theoretical considerations, the hysteretic energy‐peak deformation trend is discussed, highlighting that (a) the significant duration of the ground motion explains the variability of the hysteretic energy for a given peak deformation; (b) the hysteretic energy dissipated in an AS decreases (for a given AS peak displacement) if the peak displacement in the MS increases. A vector‐valued probabilistic seismic demand model consistent with these considerations is proposed in the form of a surface relating the hysteretic energy in the sequence to the peak deformation in the MS and a ground‐motion intensity measure of the AS. This is calibrated via sequential cloud‐based time‐history analyses. The framework is demonstrated for 14 reinforced concrete frame buildings with different height, plastic mechanisms, and infill distributions. The results show the feasibility of the proposed approach, effectively capturing damage accumulation without inconsistencies in the obtained statistical model. The framework may be used for risk‐assessment applications explicitly incorporating ground‐motion sequences. The hysteretic energy versus peak deformation relationship may also be exploited in problems involving long‐duration ground motions or soft soils.

From earthquake swarm to a main shock–aftershocks: the 2018 activity in West Bohemia/Vogtland

SUMMARYIn earthquake swarms, seismic energy is released gradually by many earthquakes without a dominant event, which offers detailed insight into the processes on activated faults. The swarm of May 2018 that occurred in West Bohemia/Vogtland region included more than 4000 earthquakes with ML = 〈0.5, 3.8〉 and its character showed significant changes during the two weeks duration: what started as a pure earthquake swarm ended as a typical main shock–aftershock sequence. Based on precise double-difference relocations, four fault segments differing in strikes and dips were identified with similar dimensions. First, two segments of typical earthquake swarm character took place, and at the end a fault segment hosting a main shock–aftershock sequence was activated. The differences were observable in the earthquakes spatio-temporal evolutions (systematic versus disordered migration of the hypocentres), b-values (>1.3 for the swarm, <1 for the main shock–aftershocks), or the smoothness of seismic moment spatial distribution along the fault plane. Our findings can be interpreted by local variations of fault rheology, differential stress and/or smoothness of the faults surface, possibly related to the crustal fluids circulating along the fault plane and their interplay with the seismic cycle.

Performance evaluation of buckling-restrained braced frames under repeated earthquakes

Structures in earthquake-prone areas are not subjected to a single seismic event, but also to a seismic sequence consisting of mainshock and several aftershocks. However, the influence of seismic sequence on performance of structures has not been addressed in majority of existing seismic codes. This paper investigates the effect of repeated earthquakes on performance of steel buckling restrained braced frames. For this purpose, 4-story and 10-story prototype buckling restrained braced frames, designed according to Iranian building codes, are exposed to five seismic sequences. Nonlinear time history analyses are conducted and the responses of frames are measured in terms of maximum inter-story and residual drifts. Furthermore, Park–Ang damage indices and global ductility factors are obtained for braced frames under examined mainshocks and mainshock–aftershock sequences. From the results of this research, it is found that the seismic sequence has the potential to increase the inter-story drift, residual drift, damage index and global ductility factor of buckling restrained braced frames. It is also highlighted that the spectral acceleration of mainshock–aftershock sequence, in comparison to that of single event mainshock, considerably affects the performance of buckling restrained braced frame under repeated earthquakes.

An Investigation of Vector Intensity Measures for Seismic Collapse Assessment Under Far-Field Aftershocks

Aftershock records have a considerable effect on the results of collapse assessments conducted on buildings. Thus, they should be selected cautiously. As the number of recorded aftershocks is not sufficient, mainshock records are often utilized instead. In order to increase the correlation between the aftershock time history and the seismic response of a structure, this research intends to investigate several Intensity Measures (IMs). For this study, three RC frames were considered. Forty-four far-field records from FEMAP-695 were selected as main and aftershock. Each building analysis was conducted under 44 mainshock–aftershock chains. According to the results, use of the summation of the first mode spectral acceleration value of aftershocks as the second part of a vector IM can lead to the sufficiency of the IM.

Identifying Optimal Intensity Measures for Predicting Damage Potential of Mainshock–Aftershock Sequences

Large earthquakes are followed by a sequence of aftershocks. Therefore, a reasonable prediction of damage potential caused by mainshock (MS)–aftershock (AS) sequences is important in seismic risk assessment. This paper comprehensively examines the interdependence between earthquake intensity measures (IMs) and structural damage under MS–AS sequences to identify optimal IMs for predicting the MS–AS damage potential. To do this, four categories of IMs are considered to represent the characteristics of a specific MS–AS sequence, including mainshock IMs, aftershock IMs (i.e., IMMS and IMAS, respectively), and two newly proposed IMs through taking an entire MS–AS sequence as one nominal ground motion (i.e., IM1MS–AS), or determining the ratio of IMAS to IMMS (i.e., IM2MS–AS), respectively. The single-degree-of-freedom systems with varying hysteretic behaviors are subjected to 662 real MS–AS sequences to estimate structural damage in terms the Park–Ang damage index. The intensities in terms of IMMS, IMAS, and IM1MS–AS are correlated with the accumulative damage of structures (i.e., DI1MS–AS). Moreover, the ratio (i.e., DI2MS–AS) of the AS-induced damage increment to the MS-induced damage is related to IM2MS–AS. The results show that IM2MS–AS exhibits significantly better performance than IMMS, IMAS, and IM1MS–AS for predicting the MS–AS damage potential, due to its high interdependence with DI2MS–AS. Among the considered 22 classic IMs, Arias intensity, root-square velocity, and peak ground displacement are respectively the optimal acceleration-, velocity-, and displacement-related IMs to formulate IM2MS–AS. Finally, two empirical equations are proposed to predict the correlations between IM2MS–AS and DI2MS–AS in the entire structural period range.

Constant-ductility energy factors of SDOF systems subjected to mainshock–aftershock sequences

This article focuses on the energy factor of single-degree-of-freedom (SDOF) systems subjected to mainshock–aftershock (MSAS) sequences, of which 163 and 143 are collected from crustal and subduction regions, respectively. The recorded MSAS sequences are divided into four groups based on the relative intensity that is defined as the ratio of the peak ground acceleration ( PGA) of an aftershock to the PGA of the corresponding mainshock. Constant-ductility inelastic spectra are calculated to assess the energy factor, γ, defined as the ratio of the covered area of the skeleton load-deformation curve of the inelastic structural system to that of the corresponding elastic system with identical elastic properties, by considering various levels of structural inelasticity. Moreover, the effect of the hysteresis law, damping ratio, post-yield stiffness ratio, soil condition, and relative intensity on the energy factor is thoroughly analyzed. A predictive model is also developed as a function of the ductility factor, vibration period, damping ratio, and post-yield stiffness ratio. Such a model is expected to facilitate the energy-based seismic design of structures.

Conditional generative adversarial network model for simulating intensity measures of aftershocks

Earthquake disaster records demonstrate that the influence of aftershocks (ASs) needs to be considered in structural seismic design and performance assessment, owing to the additional damage caused by them. To study the failure mechanism of a structure undergoing a sequence earthquake (i.e., mainshock–aftershock (MS–AS)), a clear understanding of the correlation between the intensity measures (IMs) of an MS–AS is important. However, the above correlation has not yet been systematically studied. Previously, some researchers have investigated the correlation between the individual IMs of an MS–AS separately by a Copula function based on an assumption that all the IMs of the MS (AS) are independent. However, the IMs are actually related, owing to their definition. Concurrently, deep learning (particularly the generation models) can be used to reveal the potential connections between data without any assumptions. Moreover, these models can present the conditional probability distribution of data by adding specific conditions. This study aims to build a conditional generative adversarial network (CGAN) model to simulate the IMs of an AS of an MS–AS, which can not only reflect the correlation between the corresponding IMs of the MS–AS but also that between the IMs used. The performance of this model is ascertained based on residual analysis, and the IM AS predictability is tested using real records. This study selects 972 MS–AS ground motions from the Next Generation Attenuation-West2 (NGA-West2) database, randomly dividing them into 80% and 20% and using as the training set and testing set, respectively. The results show that the CGAN model can predict the IMs of ASs with good accuracy. Moreover, the ground motion prediction equation (GMPE) by Abrahamson et al. (ASK14) is selected to compare with the CGAN model, and it is exhibited that the CGAN model matches the as-recorded IMs of ASs better that the former. All these results demonstrate that the proposed CGAN model is a promising and reliable approach for IM prediction of an AS.

A Long-Lived Swarm of Hydraulic Fracturing-Induced Seismicity Provides Evidence for Aseismic Slip

ABSTRACTSeismic swarms are defined as an increase in seismicity that does not show a clear mainshock–aftershock sequence. Typically, swarms are primarily associated with either fluid migration or slow earthquakes (aseismic slip). In this study, we analyze a swarm induced by hydraulic fracturing (HF) that persisted for an unusually long duration of more than 10 months. Swarms ascribed to fluid injection are usually characterized by an expanding seismicity front; in this case, however, characteristics such as a relatively steady seismicity rate over time and lack of hypocenter migration cannot be readily explained by a fluid-diffusion model. Here, we show that a different model for HF-induced seismicity, wherein an unstable region of a fault is loaded by proximal, pore-pressure-driven aseismic slip, better explains our observations. According to this model, the steady seismicity rate can be explained by a steady slip velocity, while the spatial stationarity of the event distribution is due to lateral confinement of the creeping region of the fault with increased pore pressure. Our results may have important implications for other induced or natural seismic swarms, which could be similarly explained by aseismic loading of asperities driven by fluid overpressure rather than the often-attributed fluid-migration model.

Short-Term Probabilistic Hazard Assessment in Regions of Induced Seismicity

ABSTRACTThis project introduces short-term hazard assessment frameworks for regions with induced seismicity. The short-term hazard is the hazard induced during the injection for hydraulic-fracturing-induced earthquakes. For wastewater-disposal-induced earthquakes, it is the hazard within a few days after an observed earthquake. In West Texas, hydraulic-fracturing-induced earthquakes cluster around the injection activities, and the earthquake occurrence varies greatly in time and space. We develop a method to estimate the hazard level at the production site during the injection, based on past injection and earthquake records. The results suggest that the injection volume has a negligible effect on short-term earthquake occurrence in this case, because injection volumes per well fall within a relatively narrow range, whereas the regional variations in seismic productivity of wells and b-values are important. The framework could be easily modified for implementation in other regions with hydraulic-fracturing-induced earthquakes. We then compare the framework with wastewater-disposal-induced earthquakes in Oklahoma–Kansas and natural earthquakes in California. We found that drivers of short-term seismic hazard differ for the three cases. In West Texas, clustered earthquakes dominate seismic hazards near production sites. However, for Oklahoma–Kansas and California, the short-term earthquake occurrence after an observed mainshock could be well described by the mainshock–aftershock sequence. For Stillwater in Oklahoma, aftershocks contribute less to the hazard than San Francisco in California, due to the high Poissonian mainshock rate. For the rate of exceeding a modified Mercalli intensity of 3 within 7 days after an M 4 earthquake, the aftershock sequence from natural earthquakes contributed 85% of the hazard level, whereas the aftershock contribution was only 60% for induced earthquakes in Oklahoma. Although different models were implemented for hazard calculations in regions with hydraulic fracturing versus wastewater injection, injection activities could be drivers of short-term hazard in both cases.

Vulnerability assessment of a high‐rise building subjected to mainshock–aftershock sequences

SummaryStrong aftershocks have the potential to further aggravate the damage state of structures, and much less attention has been given to the seismic vulnerability of high‐rise buildings than that of low‐ to medium‐rise buildings. This study assesses the seismic vulnerability of a 32‐storey frame–core tube building by performing the incremental dynamic analysis on the material‐based three‐dimensional numerical model. A storey damage model based on the material damage is developed using the weighted average method. Eighteen recorded mainshock–aftershock sequences, whose mainshock records match the target spectrum, are selected. The results indicate that the developed stroey damage model can effectively reflect the additional damage induced by aftershocks. Strong aftershocks have high potential to change the location of weak storeys. Notably, shifts of weak storeys are observed in more than 30% of aftershocks with relative spectral acceleration of 0.8. As the mainshock‐induced damage state becomes more severe, the mainshock‐damaged building becomes increasingly fragile to the aftershock excitation and more sensitive to aftershock intensities. The probability of exceeding severe damage state increases from 35.3% to 62.1% due to the effects of strong aftershocks. The results in this study can provide supports to the seismic resilience assessment of this high‐rise building.

Effects of Aftershocks on the Potential Damage of FRP-Retrofitted Reinforced Concrete Structures

This study investigates the effects of aftershocks on the potential damage of reinforced concrete (RC) structures retrofitted by fibre-reinforced polymer (FRP). An eight-storey RC frame that was poorly confined due to deficient transverse reinforcement was selected and then retrofitted by FRP wraps to provide external confinement. Inelastic time history and damage analyses of the frame under single earthquakes and mainshock–aftershock sequences were performed. FRP retrofit did not ensure a damage-free structure, and it minimised the damage though. The results indicated different contributions of aftershocks to the damage of the retrofitted frame, and this finding illustrates the limitations of current seismic codes. The damage caused by single earthquakes is proposed to be used as a criterion for dealing with the effects of aftershocks as follows. If the mainshocks cause minor or light damage, the effect of aftershocks is negligible, whereas the effect of aftershocks needs to be considered if the mainshocks cause moderate or severe damage. The outcomes of this study can be used in making decisions about whether the effects of aftershocks should be considered.

Cumulative Damage of Structures under the Mainshock-aftershock Sequences in the Near-fault Region

ABSTRACT This manuscript quantifies the effects of aftershocks with pulse characteristics on the cumulative damage of structures. The revised randomization method is developed to generate the artificial mainshock-aftershock (MSAS) ground motions showing pulse characteristics. The efficiency of period normalization is discussed from the point of view of dispersion, and the effects of the aftershocks are quantitatively studied. It is found that strong aftershock can contaminate the efficiency of period normalization, and the effects of strong aftershocks in the near-fault region on cumulative damage can exceed 20% and reach 40%. The equations are proposed for the prediction of damage induced by pulse-like MSAS sequences.

Seismic damage accumulation in multiple mainshock–aftershock sequences

SummaryEarthquakes are generally clustered, both in time and space. Conventionally, each cluster is made of foreshocks, the mainshock, and aftershocks. Seismic damage can possibly accumulate because of the effects of multiple earthquakes in one cluster and/or because the structure is unrepaired between different clusters. Typically, the performance‐based earthquake engineering (PBEE) framework neglects seismic damage accumulation. This is because (i) probabilistic seismic hazard analysis (PSHA) only refers to mainshocks and (ii) classical fragility curves represent the failure probability in one event, of given intensity, only. However, for life cycle assessment, it can be necessary to account for the build‐up of seismic losses because of damage in multiple events. It has been already demonstrated that a Markovian model (i.e., a Markov chain), accounting for damage accumulation in multiple mainshocks, can be calibrated by maintaining PSHA from the classical PBEE framework and replacing structural fragility with a set of state‐dependent fragility curves. In fact, the Markov chain also works when damage accumulates in multiple aftershocks from a single mainshock of known magnitude and location, if aftershock PSHA replaces classical PSHA. Herein, this model is extended further, developing a Markovian model that accounts, at the same time, for damage accumulation: (i) within any mainshock–aftershock seismic sequence and (ii) among multiple sequences. The model is illustrated through applications to a series of six‐story reinforced concrete moment‐resisting frame buildings designed for three sites with different seismic hazard levels in Italy. The time‐variant reliability assessment results are compared with the classical PBEE approach and the accumulation model that only considers mainshocks, so as to address the relevance of aftershocks for life cycle assessment.