Consideration of Mainshock-Aftershock Sequences into Performance-Based Seismic Engineering

AbstractThis paper presents the fragility assessment of non-seismically designed steel moment frames with masonry infills. The assessment considered the effects of multiple earthquakes on the damage accumulation of steel frames, which is an essential part of modern performance-based earthquake engineering. Effects of aftershocks are particularly important when examining damaged buildings and making post-quake decisions, such as tagging and retrofit strategy. The procedure proposed in the present work includes two phase assessment, which is based on incremental dynamic analyses of two refined numerical models of the case-study steel frame, i.e. with and without masonry infills, and utilises mainshock-aftershock sequences of natural earthquake records. The first phase focuses on the undamaged structure subjected to single and multiple earthquakes; the effects of masonry infills on the seismic vulnerability of the steel frame were also considered. In the second phase, aftershock fragility curves were derived to investigate the seismic vulnerability of infilled steel frames with post-mainshock damage caused by mainshocks. Comparative analyses were conducted among the mainshock-damaged structures considering three post-mainshock damage levels, including no damage. The impact of aftershocks was then discussed for each mainshock-damage level in terms of the breakpoint that marks the onset of exceeding post-mainshock damage level, as well as the probability of exceeding of superior damage level due to more significant aftershocks. The evaluation of the efficiency of commonly used intensity measures of aftershocks was also carried out as part of the second phase of assessment.

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Energy absorption and inelasticity distribution mechanisms in steel moment frames affected by mainshock-aftershock sequences

Structures ◽

10.1016/j.istruc.2021.06.082 ◽

2021 ◽

Vol 33 ◽

pp. 3550-3569

Author(s):

Mohammadmehdi Torfehnejad ◽

Serhan Sensoy

Keyword(s):

Energy Absorption ◽

Moment Frames ◽

Steel Moment Frames ◽

Aftershock Sequences

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Effects of mainshock-aftershock sequences on fragility analysis of RC buildings with ageing

Engineering Structures ◽

10.1016/j.engstruct.2020.111837 ◽

2021 ◽

Vol 232 ◽

pp. 111837

Author(s):

L. Di Sarno ◽

F. Pugliese

Keyword(s):

Fragility Analysis ◽

Rc Buildings ◽

Aftershock Sequences

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Seismic Damage Accumulation in Highway Bridges in Earthquake-Prone Regions

Earthquake Spectra ◽

10.1193/120812eqs347m ◽

2015 ◽

Vol 31 (1) ◽

pp. 115-135 ◽

Cited By ~ 30

Author(s):

Jayadipta Ghosh ◽

Jamie E. Padgett ◽

Mauricio Sánchez-Silva

Keyword(s):

Service Life ◽

Damage Accumulation ◽

Main Shock ◽

Prediction Models ◽

Time Window ◽

Damage Index ◽

Active Regions ◽

Highway Bridges ◽

Main Shocks ◽

Aftershock Sequences

Civil infrastructures, such as highway bridges, located in seismically active regions are often subjected to multiple earthquakes, including multiple main shocks during their service life or main shock–aftershock sequences. Repeated seismic events result in reduced structural capacity and may lead to bridge collapse, causing disruption in the normal functioning of transportation networks. This study proposes a framework to predict damage accumulation in structures subjected to multiple shock scenarios after developing damage index prediction models and accounting for the probabilistic nature of the hazard. The versatility of the proposed framework is demonstrated on a case-study highway bridge located in California for two distinct hazard scenarios: (1) multiple main shocks during the service life and (2) multiple aftershock earthquake occurrences following a single main shock. Results reveal that in both cases there is a significant increase in damage index exceedance probabilities due to repeated shocks within the time window of interest.

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Near-Fault Monitoring Reveals Combined Seismic and Slow Activation of a Fault Branch within the Istanbul–Marmara Seismic Gap in Northwest Turkey

Seismological Research Letters ◽

10.1785/0220210047 ◽

2021 ◽

Author(s):

Patricia Martínez-Garzón ◽

Virginie Durand ◽

Stephan Bentz ◽

Grzegorz Kwiatek ◽

Georg Dresen ◽

...

Keyword(s):

Seismic Gap ◽

Marmara Region ◽

Fault Rupture ◽

Aseismic Slip ◽

Near Fault ◽

Fault Monitoring ◽

Aftershock Sequences ◽

Borehole Strainmeter ◽

Seismic Moment Release ◽

Fluid Diffusion

Abstract Various geophysical observations show that seismic and aseismic slip on a fault may occur concurrently. We analyze microseismicity recordings from a temporary near-fault seismic network and borehole strainmeter data from the eastern Marmara region in northwest Turkey to track seismic and aseismic deformation around the hypocentral region of an Mw 4.5 earthquake in 2018. A slow transient is observed that lasted about 30 days starting at the time of the Mw 4.5 event. We study about 1200 microseismic events that occurred during 417 days after the Mw 4.5 event around the mainshock fault rupture. The seismicity reveals a strong temporal clustering, including four episodic seismic sequences, each containing more than 30 events per day. Seismicity from the first two sequences displayed typical characteristics driven by aseismic slip and/or fluids, such as the activation of a broader region around the mainshock and swarm-like topology. The third and fourth sequences correspond to typical mainshock–aftershock sequences. These observations suggest that slow slip and potentially fluid diffusion along the fault plane could have controlled the seismicity during the initial 150 days following the Mw 4.5 event. In contrast, stress redistribution and breaking of remaining asperities may have caused the activity after the initial 150 days. Our observation from a newly installed combined dense seismic and borehole strainmeter network follows an earlier observation of a slow transient occurring in conjunction with enhanced local seismic moment release in the same region. This suggests a frequent interaction of seismic and aseismic slip in the Istanbul–Marmara seismic gap.

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Variations of the earthquake diffusion rates in the Western Gulf of Corinth (Greece)

10.5194/egusphere-egu21-5282 ◽

2021 ◽

Author(s):

Georgios Michas ◽

Vasilis Kapetanidis ◽

George Kaviris ◽

Filippos Vallianatos

Keyword(s):

Fluid Pressure ◽

Stress Transfer ◽

The European Union ◽

Triggering Mechanism ◽

Development Education ◽

Seismic Sequences ◽

Gulf Of Corinth ◽

Aftershock Sequences ◽

Triggering Mechanisms ◽

Diffusion Rates

Earthquake diffusion is frequently observed in the spatiotemporal evolution of seismic clusters and regional seismicity, a characteristic that is attributed to a triggering mechanism, such as fluid flow, aseismic creep and/or stress transfer effects. In this work, we study the earthquake diffusion properties in the Western Gulf of Corinth (central Greece), an area that presents high extension rates, moderate to large magnitude earthquakes, intense microseismicity and frequent seismic swarms. We focus on the period 2013&#8211;2014 that is characterized by intense background microseismic activity along with significant seismic sequences. More specifically, the latter include the 2013 Helike swarm, the 2014 seismic sequence between Nafpaktos and Psathopyrgos, which culminated with an Mw 4.9 event on 21 September 2014, as well as moderate magnitude events that were followed by aftershock sequences. In the herein analysis, we employ a relocated earthquake catalogue of ~9000 events which delineates the activated areas during the study period in high-resolution. We consider the most significant seismic sequences and calculate their respective spatial correlation histograms and the evolution of the mean squared distance of the hypocenters with time, in order to study the earthquake diffusion rates and possible variations that might be related to the triggering mechanisms of seismicity. Our results demonstrate a weak earthquake diffusion process, analogous to subdiffusion within a stochastic framework, for the seismic sequences under consideration, providing further evidence for slow earthquake diffusion in regional and global seismicity. In addition, the earthquake diffusion rates exhibit variations that can be associated with the triggering mechanism. In particular, seismic sequences which are related with pore-fluid pressure diffusion present considerably higher diffusion rates than mainshock/aftershock sequences or the background activity. Such results may provide novel constraints on the triggering mechanisms of clustered seismic activity based on the study of the earthquake diffusion rates.&#160;AcknowledgementsWe would like to thank the personnel of the Hellenic Unified Seismological Network (http://eida.gein.noa.gr/) and the Corinth Rift Laboratory Network (https://doi.org/10.15778/RESIF.CL) for the installation and operation of the stations used in the current article. The present research is co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme &#171;Human Resources Development, Education and Lifelong Learning 2014-2020&#187; in the context of the project &#8220;The role of fluids in the seismicity of the Western Gulf of Corinth (Greece)&#8221; (MIS 5048127).

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Estimates of velocity structure and source depth using multiple P waves from aftershocks of the 1987 Elmore Ranch and Superstition Hills, California, earthquakes

Bulletin of the Seismological Society of America ◽

10.1785/bssa0810020508 ◽

1991 ◽

Vol 81 (2) ◽

pp. 508-523

Author(s):

Jim Mori

Keyword(s):

Velocity Structure ◽

Velocity Model ◽

P Wave ◽

Sediment Layer ◽

Source Depth ◽

Imperial Valley ◽

P Waves ◽

Main Shocks ◽

Aftershock Sequences ◽

Event Record

Abstract Event record sections, which are constructed by plotting seismograms from many closely spaced earthquakes recorded on a few stations, show multiple free-surface reflections (PP, PPP, PPPP) of the P wave in the Imperial Valley, California. The relative timing of these arrivals is used to estimate the strength of the P-wave velocity gradient within the upper 5 km of the sediment layer. Consistent with previous studies, a velocity model with a value of 1.8 km/sec at the surface increasing linearly to 5.8 km/sec at a depth of 5.5 km fits the data well. The relative amplitudes of the P and PP arrivals are used to estimate the source depth for the aftershock distributions of the Elmore Ranch and Superstition Hills main shocks. Although the depth determination has large uncertainties, both the Elmore Ranch and Superstition Hills aftershock sequences appear to have similar depth distribution in the range of 4 to 10 km.

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