Ground Shaking Research Articles

Seismic Velocity Recovery in the Subsurface: Transient Damage and Groundwater Drainage Following the 2015 Gorkha Earthquake, Nepal

AbstractShallow earthquakes frequently disturb the hydrological and mechanical state of the subsurface, with consequences for hazard and water management. Transient post‐seismic hydrological behavior has been widely reported, suggesting that the recovery of material properties (relaxation) following ground shaking may impact groundwater fluctuations. However, the monitoring of seismic velocity variations associated with earthquake damage and hydrological variations are often done assuming that both effects are independent. In a field site prone to highly variable hydrological conditions, we disentangle the different forcing of the relative seismic velocity variations δv retrieved from a small dense seismic array in Nepal in the aftermath of the 2015 Mw 7.8 Gorkha earthquake. We successfully model transient damage effects by introducing a universal relaxation function that contains a unique maximum relaxation timescale for the main shock and the aftershocks, independent of the ground shaking levels. Next, we remove the modeled velocity from the raw data and test whether the corresponding residuals agree with a background hydrological behavior we inferred from a previously calibrated groundwater model. The fitting of the δv data with this model is improved when we introduce transient hydrological properties in the phase immediately following the main shock. This transient behavior, interpreted as an enhanced permeability in the shallow subsurface, lasts for ∼6 months and is shorter than the damage relaxation (∼1 yr). Thus, we demonstrate the capability of seismic interferometry to deconvolve transient hydrological properties after earthquakes from non‐linear mechanical recovery.

Study on Design of Highrise Steel Building Frames and Its Seismic Evaluation

Abstract: Seismic Response Analysis of the given structural system is considered to be a subset of stability and configurationally analysis of the system. It is subjected under the calculations obtained in the form of structural response of the buildings produced by the earthquakes. It is found to be the essential and prime component of the designing phenomenon of the structures, or assessment of structural configuration and as a retrofit for the seismic prone regions of the India. The most severe types of earthquakes are essentially emerged closely nearer to the boundaries of the tectonic plates that are covered in the form of globe surface. These plates tries to move with respect one another in the form of relative motion but are resisted by doing so in terms of generation of friction until or unless the various stresses produced between the plates under epicenter reach to such a extent that the movement between the plates gets generated suddenly, which is termed as the earthquake. The local shock produces waves inside the ground which further propagates towards the surface of earth by the movement creation at the structural bases. The intensity of waves decreases with the propagation of distance as we move away from the point of epicenter. Hence, it results into the formation and existence of such regions on the earth surface having very high or less risk of seismic assessment, which indirectly depends upon the proximity to the main tectonic plates boundaries. Apart from the major earthquakes that generally exists near the boundaries of tectonic plates, there are some other earthquakes, that may have their origin and formation at the interior parts of tectonic plates nearer to the fault lines. Such kind of earthquakes are Called as Intra-plate earthquakes. These earthquakes consist of lesser energy, but may be destructive to the area nearer to the point of epicenter The earthquake imparts the action towards the structure in the form of shaking of ground and its motion in the form of vertical and horizontal components. The horizontal component consists of very high strength and the structures are usually designed to resist gravitational forces than horizontal forces, and as a results, it is the most severe component. The vertical components of the earthquake force are found to be 50% of its value in horizontal direction except in the region of point of epicenter because in the region of point of epicenter, both the components are of same orders.

System-Wide Seismic Risk Assessment of Port Facilities; Application to the Port of Thessaloniki, Greece

Damages in port facilities during past seismic events have led to widespread direct and indirect losses, with serious impact on the economic, operational, and emergency management of the port itself and, as a consequence, on the related society. Ground shaking is among the most widespread sources of seismic damage to port structures and infrastructure, together with the induced phenomena principally associated with the liquefaction of loose, saturated soils that often prevail in coastal areas. This study presents a methodology for the seismic risk assessment of port facilities which considers the combined effects of ground shaking and liquefaction as well as various interdependencies among port elements, which affect the port’s operation and, consequently, the total risk impact. The methodology, based on either probabilistic or deterministic scenario-based approaches, is demonstrated through an application to the Thessaloniki port, one of the most important ports in Southeastern Europe and the largest transit-trade port in Greece. The systemic risk analysis of the port is carried out using as a performance indicator the reduction in the container and bulk cargo movements affected by the seismic performance of the piers, the waterfront, and container/cargo handling equipment, as well as their interaction with the seismic performance of the electric power system. Two different functionality analyses of the port system are performed, one basic and one less conservative alternative. The results of the probabilistic seismic risk assessment are illustrated in terms of annual probabilities of collapse and loss exceedance curves for each individual port component as well as normalized performance loss for the whole port system for the container and cargo terminal. For the scenario-based deterministic approach, the results are given in terms of risk maps presenting the spatial distribution of damages/losses for all components as well as in terms of the expected loss of performance of the port system. The proposed methodology may provide the basis for an efficient seismic risk management of ports. It may also be adjusted and applied to other port infrastructures in Greece and worldwide considering additional components, interactions among elements, and different earthquake induced hazards.

Neural Network-Based Strong Motion Prediction for On-Site Earthquake Early Warning

Developing on-site earthquake early warning systems has been a challenging problem because of time limitations and the amount of information that can be collected before the warning needs to be issued. A potential solution that could prevent severe disasters is to predict the potential strong motion using the initial P-wave signal and provide warnings before serious ground shaking starts. In practice, the accuracy of prediction is the most critical issue for earthquake early warning systems. Traditional methods use certain criteria, selected through intuition or experience, to make the prediction. However, the criteria thresholds are difficult to select and may significantly affect the prediction accuracy. This paper investigates methods based on artificial intelligence for predicting the greatest earthquake ground motion early, when the P-wave arrives at seismograph stations. A neural network model is built to make the predictions using a small window of the initial P-wave acceleration signal. The model is trained by seismic waves collected from 1991 to 2019 in Taiwan and is evaluated by events in 2020 and 2021. From these evaluations, the proposed scheme significantly outperforms the threshold-based method in terms of its accuracy and average leading time.

Simple approach to evaluate the influence of seismic residual displacements on post-liquefaction settlements of RC-frames

Residual permanent displacements generally characterize the status of structures at the end of severe earthquake events because of large inelastic deformations demand. When the structure is founded on soils susceptible to liquefaction phenomenon, this status could particularly influence the subsequent damages due to the occurrence of liquefaction induced vertical settlements. As a consequence, the correct prediction of the effects of earthquake induced liquefaction on the built environment must consider the residual displacements induced by the ground shaking. To this aim, the paper proposes a simplified approach to evaluate the seismic response of RC frames based on a four-steps procedure composed of a set of nonlinear static analyses reproducing a sequential process of a ground shaking followed by a liquefaction induced ground settlements. The novelty of the proposal is to carry out sequential nonlinear static analyses by preserving the status of the RC frame at the end of the seismic event in terms of residual displacements and then to directly consider their influence on the subsequent analysis simulating the occurrence of post-liquefaction vertical settlements.A parametric study has been developed by means of numerical analyses, referring to two RC frames derived from literature, in order to highlight the relevance of the seismic residual displacements on the damage induced by the subsequent vertical settlements due to soil liquefaction. The proposed simplified approach has then been validated through more sophisticated nonlinear dynamic time-history analyses. The results presented in the paper underline the efficacy of the proposed approach, the simplicity in implementing the four-steps procedure and the lower computational effort with respect to nonlinear dynamic time-history analyses.

Partitioning Ground Motion Uncertainty When Conditioned on Station Data

ABSTRACT Rapid estimation of earthquake ground shaking and proper accounting of associated uncertainties in such estimates when conditioned on strong-motion station data or macroseismic intensity observations are crucial for downstream applications such as ground failure and loss estimation. The U.S. Geological Survey ShakeMap system is called upon to fulfill this objective in light of increased near-real-time access to strong-motion records from around the world. Although the station data provide a direct constraint on shaking estimates at specific locations, these data also heavily influence the uncertainty quantification at other locations. This investigation demonstrates methods to partition the within- (phi) and between-event (tau) uncertainty estimates under the observational constraints, especially when between-event uncertainties are heteroscedastic. The procedure allows the end users of ShakeMap to create separate between- and within-event realizations of ground-motion fields for downstream loss modeling applications in a manner that preserves the structure of the underlying random spatial processes.

Case study of large-scale levee failures induced by cyclic softening of clay during the 2016 Meinong earthquake

The 2016 Meinong earthquake (Meinong EQ) caused a serious disaster, including many liquefaction-induced damages, in southern Taiwan. This study investigated the “flow-like” failure of Rixin levee during the Meinong EQ through field exploration, laboratory test, and numerical analysis. The failure mechanism of soil liquefaction, however, failed to explain the case of Rixin levee because the levee foundation where the failure occurred was primarily composed of clayey soil. Therefore, the cyclic softening of clayey soil subjected to ground shaking was considered a key factor that induced the damage. Site characterization, liquefaction analysis, seepage analysis, slope stability analysis, and dynamic analysis indicated that when the strength reduction of Rixin levee (approximately 10%–15%) due to cyclic softening was accounted for during the 2016 Meinong EQ, the displacement of the embankment estimated using the Newmark sliding block method and finite element method was in line with the observed damage of the levee. The analysis procedure was validated with the case of the 2010 Jiasian earthquake, in which no failure occurred at the site under similar shaking.

Development of a seismic site-response zonation map for the Netherlands

Abstract. Earthquake site response is an essential part of seismic hazard assessment, especially in densely populated areas. The shallow geology of the Netherlands consists of a very heterogeneous soft sediment cover, which has a strong effect on the amplitude of ground shaking. Even though the Netherlands is a low- to moderate-seismicity area, the seismic risk cannot be neglected, in particular, because shallow induced earthquakes occur. The aim of this study is to establish a nationwide site-response zonation by combining 3D lithostratigraphic models and earthquake and ambient vibration recordings. As a first step, we constrain the parameters (velocity contrast and shear-wave velocity) that are indicative of ground motion amplification in the Groningen area. For this, we compare ambient vibration and earthquake recordings using the horizontal-to-vertical spectral ratio (HVSR) method, borehole empirical transfer functions (ETFs), and amplification factors (AFs). This enables us to define an empirical relationship between the amplification measured from earthquakes by using the ETF and AF and the amplification estimated from ambient vibrations by using the HVSR. With this, we show that the HVSR can be used as a first proxy for site response. Subsequently, HVSR curves throughout the Netherlands are estimated. The HVSR amplitude characteristics largely coincide with the in situ lithostratigraphic sequences and the presence of a strong velocity contrast in the near surface. Next, sediment profiles representing the Dutch shallow subsurface are categorised into five classes, where each class represents a level of expected amplification. The mean amplification for each class, and its variability, is quantified using 66 sites with measured earthquake amplification (ETF and AF) and 115 sites with HVSR curves. The site-response (amplification) zonation map for the Netherlands is designed by transforming geological 3D grid cell models into the five classes, and an AF is assigned to most of the classes. This site-response assessment, presented on a nationwide scale, is important for a first identification of regions with increased seismic hazard potential, for example at locations with mining or geothermal energy activities.

Using LSTM Neural Networks for Onsite Earthquake Early Warning

Abstract Onsite earthquake early warning (EEW) systems determine possible destructive S waves solely from initial P waves and issue alarms before heavy shaking begins. Onsite EEW plays a crucial role in filling in the blank of the blind zone near the epicenter, which often suffers the most from disastrous ground shaking. Previous studies suggest that the peak P-wave displacement amplitude (Pd) may serve as a possible indicator of destructive earthquakes. However, the attempt to use a single indicator with fixed thresholds suffers from inevitable errors because the diversity in travel paths and site effects for different stations introduces complex nonlinearities. In addition, the short warning time poses a threat to the validity of EEW. To conquer the aforementioned problems, this study presents a deep learning approach employing long short-term memory (LSTM) neural networks, which can produce a highly nonlinear neural network and derive an alert probability at every time step. The proposed LSTM neural network is then tested with two major earthquake events and one moderate earthquake event that occurred recently in Taiwan, yielding the results of a missed alarm rate of 0% and a false alarm rate of 2.01%. This study demonstrates promising outcomes in both missed alarms and false alarms reduction. Moreover, the proposed model provides an adequate warning time for emergency response.

Near‐Fault Ground Motion Impacts on High‐Speed Rail Large‐Span Continuous Girder Bridge considering Pile‐Soil Interaction

This paper examines and discusses the dynamic response of a high‐speed train‐bridge‐soil‐pile foundation system to near‐fault earthquakes. A 72 + 120 + 72 m continuous girder bridge of a high‐speed railroad was selected as the model for calculation. Based on the p‐y model for simulating pile‐soil interaction, the moment‐curvature analysis program XTRACT is used to calculate the moment and curvature of bridge piers and pile foundation sections, and the finite element (FE) software is used to establish two nonlinear global bridge models under seismic effects in the high‐intensity zone, one considering pile‐soil interaction and one without considering pile‐soil interaction. The Ap/Vp parameter, the ratio of peak acceleration to peak velocity of transverse ground shaking, is used to reflect the impulse characteristics of earthquakes and the effect of the Ap/Vp parameter on the dynamic response of bridges to earthquakes was studied. The elastic‐plastic response of the bridge system was calculated under lateral and vertical near‐fault (NF) impulse/NF nonimpulse/far‐field (FF) ground motions (GMs). The study shows that the structural displacement increases, and the internal force decreases after considering the pile‐soil interaction. The results show that the bridge piers enter the elastoplastic phase under rare earthquakes. The NF ground shaking couples with the bridge into the elastoplastic phase with a more significant impulse period than the FF ground shaking intensifies the dynamic response of the bridge structure.

Seismic Performance of R. C. Elevated Water Storage Tanks

The primary basis for construction of structures for strong ground shaking is that it shall not collapse. However, permissible damage for structural components is permitted. If a structure is permitted to be damaged in the case of severe ground shaking, it shall be constructed for seismic forces considerably lesser than those expected in the event of severe shaking if it is to remain linearly elastic. Response reduction factor, R is the factor that should be used to lower the actual base shear in order to obtain the required design lateral force. In the case of seismic design of water tanks, different values of the “R” factor are suggested by various countries, such as IBC-2000 gives the value of the “R” factor varying from 2 to 4, whereas ACI 350.3 has given the values from 2 to 4.5, whereas AWWA (D-100) recommended the values in between 3 and 4. According to Eurocode 8, the behaviour factor, also known as the “R” factor, varies between 1 and 5. The values in the Indian code for seismic analysis, IS1893-(Part 2), range from 2 to 4.Hence, it is tempting to look into the real aspect of the ‘R’ factor evaluation. IS 1893, an Indian seismic code, calculates a design shear force for an elastic structure and divides it by twice R. In other words, the term “R” refers the amount of over-strength and ductility that a structure is predicted to possess. Thus, by considering the elements, over strength factor, redundancy factor, and ductility factor, the structure can be constructed for much lesser force than is predicted by the violent shaking, preventing the structure from collapsing. Available literature shows a sound recommendation does not exist for the values of “R” given in the seismic design codes of various countries, including India. There is currently no basis for the R-values in the codes. According to the available literature, limited research has been done on the influence of viscous dampers on “R,” which reflects a structure's ability of dissipation of energy through inelastic behaviour. The finite element (FE) approach must be used in conjunction with the study of material properties, the study of nonlinear hinge properties, the investigation of the seismic response of water tanks for different water heights, and the effect of including braces in staging to reduce the seismic response of the water tank to examine the nonlinear response of tanks under dynamic time-history and push-over analysis.

Spatiotemporal changes in seismic velocity associated with hydraulic fracturing-induced earthquakes near Fox Creek, Alberta, Canada

To characterize the subsurface geomechanical response to hydraulic fracturing (HF) activities, we study the spatiotemporal changes of seismic velocity during the completion of four HF wells in the Fox Creek area, Alberta, Canada. We estimate temporal velocity changes (dv/v) from ambient seismic noise recorded during the Tony Creek Dual Microseismic Experiment (ToC2ME) by comparing a 5-day stacked noise correlation function with a reference noise correlation function stacked over the deployment period. In the frequency band (0.1–0.4 Hz) most sensitive to the injection depths (~3.4 km), we observe daily dv/v that revealed alternating gradual velocity decreases and increases with magnitudes in the range of ±0.9%. We found a strong temporal correlation between the onset of velocity decreases and periods of intense seismicity, suggesting that the observed dv/v reductions are likely caused by stress-induced subsurface deformation due to elevated pore pressures, increased crack density, and ground shaking. A period of dv/v increase observed between the beginning and end of different well stimulation is attributed to crustal healing. Comparing the dv/v time series with injection parameters, we observed a 272.66% increase in induced seismicity and 50% more reduction in dv/v during the second injection phase that are correlated with 90.53%, 169.64%, and 4.34% increase in the injection volume, rate, and pressure, respectively. Our study provides valuable new information on the changes in reservoir elastic properties within the Western Canadian Sedimentary Basin. It also demonstrates that coda wave interferometry using data from dense seismic arrays near injection sites can be an additional tool for monitoring hydraulic fracturing operations.

Sismotool: A New Tool to Simulate Ground Shaking and Earthquake Losses

Sismotool: A New Tool to Simulate Ground Shaking and Earthquake Losses

The 2019 Le Teil surface-rupturing earthquake along the La Rouvière Fault within the Cévennes fault system (France): What does paleoseismology reveal?

The 2019-11-1, Mw4.9 Le Teil earthquake occurred within the NE termination of the Cévennes faults system (CFS) in southern France, along the La Rouvière fault (LRF), an Oligocene normal fault which was not known to be potentially active. This shallow moderate magnitude reversefaulting event produced a 5 km-long surface rupture and strong ground shaking. No evidence of previous quaternary activity was observed in the morphology, raising the question whether the fault had been reactivated for the first time since the Oligocene or had broken the surface in the past without being detected in the morphology. To address this issue, we carried out paleoseismological investigations to analyze and characterize evidences of paleo-ruptures in Quaternary deposits. We discovered that at least one event prior 2019, occurred between 13.5 and 3.3 ka within the central part of the fault segment that broke in 2019, and that a possible earlier surfacerupturing event occurred within the northern part of this segment during the 16th century. Further investigations coupling sub-surface geophysical investigations and trenching are now carried out within the southern and northern segments of the LRF as well as along the other fault segments of the CFS.

A new tool to simulate ground shaking and earthquake losses

The main purpose of this suite is Planning and Management of Seismic Emergencies before and after future damaging earthquake. This tool is written in ArcGIS software executing a fast and efficient determination of the estimated shakemaps and damage scenarios. The tool allows to select the earthquake source parameters through a defined database; moreover ground motion prediction equations can be chosen and they can be combined according to the study area features. The local site effects are characterized from Vs30 values, which have been achieved by topographic slope as a proxy (even with local correlations) obtained from digital elevation model. The elements exposed to risk are incorporated from the cadastral database after inputs has been refined through an automated analysis. Vulnerability and estimated losses can be determined either empirically (EMS-98 scale and Vulnerability Index, Iv) or analytically (Capacity spectrum). Additionally, a vulnerability modifier is implemented to account soil-structure resonance. Epistemic uncertainties are quantified in the input parameters using a logic tree. This tool has been validated through a representative seismic scenario: the 1910 Adra earthquake (southern Spain) with moment magnitude (Mw) 6.3 and macroseismic intensity VIII (EMS-98 scale) proving the reliability of this program

Investigation on Seismic Response of Long‐Span Special Steel Truss Cable‐Stayed Bridge

Due to the small self‐weight of the steel truss cable‐stayed bridge with a single tower and a single cable plane, the torsional stiffness and wind stability of the structure are reduced. The arrangement of the deck type makes the mechanical properties of the cable‐stayed bridge more complicated while reducing the cost and increasing the aesthetics. The effects of structural parameter variations and traveling wave effects on the seismic response of this steel truss cable‐stayed bridge with a single tower and a single cable plane were investigated by the nonlinear time‐history analysis method and nonuniform seismic analysis method. The results show that the displacement of the floating system under seismic action is larger than the other three systems, but its internal force is significantly smaller than the other three systems. The spectral characteristics and the duration of ground shaking have a greater influence on the maximum bending moment values corresponding to the height of the cable tower and the maximum axial force values of the main girder bars corresponding to the length of the bridge under earthquake action. The effect of steel truss girder stiffness parameter variations on structural internal forces of bridges and the effect of traveling wave effects on structural displacements of bridges in specific apparent wave velocity intervals do not exist universally.

Применение методов геоинформатики для изучения и оценивания риска последствий землетрясений

The struggle of mankind against the consequences of strong and catastrophic earthquakes has been going on throughout its history, and so far, success in this field is rather modest. This is due to the complexity and inaccessibility of objects for studying deep geological processes that lead to defor-mation and destruction of the Earth's crust, in which seismicity is manifested. Earthquake risk assess-ment for earthquake mitigation is one of the most important issues for a country where such natural disasters can occur. Tectonic and structural-geological studies using modern space remote sensing tools and their integration with spatial data in a geographic information system (GIS) environment are becoming increasingly popular among scientists. Ruptures and associated surface deformation due to ground shaking can be observed with remote sensing data. The use of remote sensing methods to rec-ognize the displacement of faults was carried out in Isfahan (Iran). Based on the obtained data, a map of seismic activity was compiled with field checks and laboratory data analysis. Thus, the purpose of the article is to show the possibilities of geoinformatics for the study of earthquakes. This will increase resilience to future earthquakes, especially for those historic buildings and bridges that are over 400 years old.

Spatiotemporal Evolution of Ground-Motion Intensity at the Irpinia Near-Fault Observatory, Southern Italy

ABSTRACT Fault zones are major sources of hazard for many populated regions around the world. Earthquakes still occur unanticipated, and research has started to observe fault properties with increasing spatial and temporal resolution, having the goal of detecting signs of stress accumulation and strength weakening that may anticipate the rupture. The common practice is monitoring source parameters retrieved from measurements; however, model dependence and strong uncertainty propagation hamper their usage for small and microearthquakes. Here, we decipher the ground motion (i.e., ground shaking) variability associated with microseismicity detected by dense seismic networks at a near-fault observatory in Irpinia, Southern Italy, and obtain an unprecedentedly sharp picture of the fault properties evolution both in time and space. We discuss the link between the ground-motion intensity and the source parameters of the considered microseismicity, showing a coherent spatial distribution of the ground-motion intensity with that of corner frequency, stress drop, and radiation efficiency. Our analysis reveals that the ground-motion intensity presents an annual cycle in agreement with independent geodetic displacement observations from two Global Navigation Satellite System stations in the area. The temporal and spatial analyses also reveal a heterogeneous behavior of adjacent fault segments in a high seismic risk Italian area. Concerning the temporal evolution of fault properties, we highlight that the fault segment where the 1980 Ms 6.9 Irpinia earthquake nucleated shows changes in the event-specific signature of ground-motion signals since 2013, suggesting changes in their frictional properties. This evidence, combined with complementary information on the earthquake frequency–magnitude distribution, reveals differences in fault segment response to tectonic loading, suggesting rupture scenarios of future moderate and large earthquakes for seismic hazard assessment.

Remote Triggering of Damage Followed by Healing Recorded in Groundwater Pressure

Water levels in three adjacent water wells in the Yarmouk Gorge area have all responded to the 2020 Elazığ Mw 6.8 teleseismic earthquake. Water levels in two aquifers exhibited reciprocal behavior: during the first eight days after the earthquake, water level decreased by 40 cm in the deeper highly confined aquifer, and increased by 90 cm in the shallower less confined aquifer. The recovery of the water levels in both aquifers continued for at least three months. We interpret these observations as reflecting the increase in damage along the fault at the Yarmouk Gorge. Ground shaking increased the damage and permeability of this fault, temporarily connecting the two aquifers, allowing flow from the deep aquifer to the shallow one. Model results showing decreased permeability suggest that the fault healed by one order of magnitude within three days. This is the first documentation of decrease in permeability in a fault zone within such short time scales.

Reliability of structural wall shear design for tall reinforced-concrete core wall buildings

The developments of shear design acceptance criterion for structural walls in tall reinforced-concrete core wall buildings were reviewed and reliability studies were conducted. Over the past 10 years, the seismic action portion of the shear design acceptance criterion has consistently been in the general format of γFu ≤ ϕFn,e, where γ is the demand factor, Fu is the mean shear demand resulting from a suite of ground motions, Fn,e is the nominal shear strength computed from expected material properties, and ϕ is the uncertainty in Fn,e. Between the governing code, ASCE7-16, and the tall building guidelines, PEER TBI (2010, 2017) and LATBSDC (2011, 2014, 2017, 2020), there has been a lack of consensus in the recommendations for γ and ϕ factors. Thus, reliability studies were conducted on the shear design acceptance criterion, with 20- and 30-story case study buildings designed and analyzed per LATBSDC (2014) guidelines. Using closed-form solutions and Monte Carlo simulations, for the range of f’c considered, the shear design acceptance criterion using γ = 1.5, ϕ = 1.0, and a conservative dispersion in shear demand of ρD = 0.50 resulted in at least 94.2% reliability, conditioned upon MCE hazard level ground shaking, suggesting that the current LATBSDC (2020) recommendations provide adequate safety. For a reduction in safety (e.g., use of γ < 1.5), further reliability studies including a larger population of tall buildings will be needed to calibrate γ and ϕ factors.