Fault-parallel Components Research Articles

Investigating seismic performance of SMRF buildings under subshear and supershear rupture conditions: Assessment of storey-level internal damage

The source effect of earthquake ruptures causes spatial-temporal variability in ground motion characteristics in the vicinity of a fault. This research employs a dynamic rupture-based method with SPECFEM3D to simulate two rupture types: subshear and supershear. While the former depends on the rupture length of the fault, the latter depends on the rupture velocity. Synthetic earthquake ground motion data are generated across the entire domain, encompassing both near-fault and far-fault locations. Ground motions exhibit multidimensionality, with subshear effects evident in the fault normal component and supershear effects distinctly reflected in the fault parallel component. These ground motions have been employed to excite low (S1L), mid (S1M), and high-rise (S1H) steel special moment resisting frame (SMRF) buildings modelled using the modified Ibarra-Medina-Krawinkler (IMK) analogy. Understanding the far-field effects of supershear earthquakes and the near-field effects of directivity in subshear earthquakes on the structural response of SMRF buildings has been aided by several engineering demand parameters (EDPs), including floor acceleration, interstorey-drift ratio, and roof drift ratio.

Influence of rupture velocity on risk assessment of concrete moment frames: Supershear vs. subshear ruptures

The possibility of ground motions propagating at speeds greater than the Rayleigh wave speed was accepted not long ago, and thus studies on them are limited. These supershear motions are believed to damage specific kinds of infrastructure, and thus studying the risk associated is important. As a part of this investigation, we use state-of-the-art tools from the Natural Hazards Engineering Research Infrastructure to estimate normalized economic losses and injuries, by considering one particular building type and occupancy category listed in HAZUS-MH. Faults of similar dimensions are shown to replicate subshear and supershear earthquake instances with four groups of station points parallel to the fault and four more perpendicular to the fault. Both fault parallel and fault normal components of ground motion are stimulated. The economic loss % and injury is standardized in metrics of repair cost and population respectively and is estimated along with the associated uncertainty for 3, 6 and 9-story commercial concrete moment frame structures. Inclusion of complex phenomena such as supershear earthquake events in evaluating economic losses and risk will contribute to the United Nation Office for Disaster Risk Reduction (UNDRR) vision of disaster-resilient development goals.

Significance of Pulse-Like Ground Motions and Directivity Effects in Moderate Earthquakes: The Example of the Mw 6.1 Gölyaka-Düzce Earthquake on 23 November 2022

ABSTRACT The 1400 km long North Anatolian Fault Zone in Türkiye runs through numerous densely populated regions, including the city of Düzce that was recently hit by an Mw 6.1 earthquake on 23 November 2022. This was the first moderate event in the region after the devastating Mw 7.2 earthquake in 1999, which cost the lives of over 700 people. Despite its moderate size, the earthquake caused unexpected severe damage to a significant number of buildings, as reported by local institutions (Disaster and Emergency Management Presidency, AFAD). It is well established that ground motions in the near field can lead to increased damage due to near-field domain effects, such as ground-motion pulses and directivity effects (i.e., when the site is aligned with rupture propagation). We examine potential near-field effects using the strong ground motion database of AFAD-Turkish Accelerometric Database and Analysis Systems. To achieve this, we first analyze the behavior of the ground-motion intensities in terms of their spatial distribution and observe higher peak ground velocity than expected by ground-motion models in spatially constrained azimuthal ranges. Furthermore, we find that the majority of the near-fault recordings contain velocity pulses that are primary concentrated on the fault-parallel component. This outcome questions the widely accepted understanding from the previous studies, which mainly suggested that impulsive ground motions that are associated with directivity effects primarily occur on the fault-normal component of large-magnitude events.

Spatial variation of structural fragility due to supershear earthquakes

Collapse fragility of structures is studied using equipotent subshear and supershear earthquakes. Supershear earthquakes propagate at a speed faster than the shear-wave speed of the medium, thereby producing significantly different ground motion characteristics than subshear ruptures. In particular, fault parallel component dominance is established in the literature for supershear events. By considering a set of stations parallel to the strike of the fault, and another set perpendicular to the strike of the fault at various distances, fragility curves are derived as a function of distance from the fault in the near-field. In addition, the fault-parallel and fault-normal components in the near-field are applied separately to single-degree-of-freedom systems with peak-oriented modified Ibarra–Medina–Krawinkler hysteretic behaviour to characterize the component-wise differences across the subshear and supershear cases. A comparison of the median fragilities with HAZUS suggested values of similar structural systems is also presented.

Offshore wind turbine subjected to supershear earthquake ruptures

Supershear earthquakes, analogous to supersonic speeds of sounds, show the presence of a Mach front in the top view. This feature was observed in several past earthquakes, including the 1999 Izmit earthquake, 2001 Kokoxili earthquake, to name a few. The ground motion from supershear ruptures can be destructive to structures due to dominant fault-parallel components. In this study, we demonstrate the effect of supershear ruptures on wind turbines by modelling them in OpenSees. Earthquake ruptures are simulated using SPECFEM3D, another open-source software. By considering arrays at different offsets along strike and away from the strike, the distance effect on serviceability limit states of wind turbines is studied using supershear and subshear earthquakes.

Response of inelastic SDOF systems subjected to dynamic rupture simulations involving directivity and fling step

Directivity is a phenomenon perceived during fault ruptures wherein the ground motion and spectral response in the direction of the rupture is more significant than in any other direction. The objective of this study is to evaluate the variability in characteristics of near-fault ground motions as well as the ductility demand on structures due to directivity based on simulations of strike-slip earthquake events by employing SPECFEM3D, a physics-based ground motion simulation code. To understand the finite fault propagation effect, a source effect, the vertical strike-slip fault is considered to be embedded in an elastic half-space, to prevent the influence of path and site effects. Two scenarios are designed based on the positioning of nucleation asperity (NA): (1) in the middle of the fault face to simulate bilateral (BL) rupture and (2) shifted to one end for the case of unilateral (UL) rupture. The ground motions at near-fault stations, located in a racetrack configuration around the surface trace of the fault, are analyzed. In addition to a high spectral content in the forward directivity stations as a result of UL rupture, directivity velocity pulses identified in the fault-normal components are higher than the fling step velocity pulses in the fault-parallel component for the racetrack stations considered. Furthermore, the study examines the correlation between ductility demands computed based on elastoplastic rheology with direct point parameter and ground motion intensity measures for directivity and fling step stations.

A Modified Algorithm to identify the strongest velocity pulse in three orthogonal components of ground motions

An algorithm for the identification of the strongest velocity pulse is proposed based on wavelet analysis, which considers three orthogonal components of the ground motion. According to the NGA-West2 database, 6288 strong motion records were analyzed, and further, the classification results were compared with those obtained from the existing identification method of Shahi and Baker (2014) [1]. Among the results, our algorithm classified more records as pulse-like ground motion and has expanded the pulse identifications. In other words, the proposed algorithm can reflect the three orthogonal characteristics of the original ground motion records. Besides, the relationships of pulse amplitude, period with magnitude and fault distance were analyzed. Based on the analysis of near-fault ground motions containing velocity pulses, the following conclusions can be made: (1) The peak of the strongest velocity pulse gradually reduces with the increase of the fault distance, while gradually rises with the increase of the magnitude. Comparing with the fault normal or fault parallel orientation component, the strongest velocity pulse component has larger energy and smaller peak velocity. (2) For the relationship between the velocity pulse period and magnitude, results show that when Mw < 7, the predicted value of our model is larger than that of the Shahi and Baker (2014) [1] model; however when Mw ≥ 7, the prediction results from these two models are fairly close. The difference between the two models decreases as magnitude increases. That is because the strongest velocity pulses occupied more in the horizontal direction under a large magnitude.

Late Pleistocene slip rate of the Chaman fault based on 10Be exposure dating of offset geomorphic surfaces near Kabul, Afghanistan

We report the first late Pleistocene left-lateral slip rate of the northern Chaman fault in Afghanistan based on 10Be dating of offset alluvial fan surfaces. Field mapping complemented with the analysis of CORONA and ALOS PRISM satellite images and shaded relief and topographic data allows us to identify piercing points across the fault zone at two displaced alluvial fans (Ghat Bandakul and Azadkhail) at Wardak Province south of Kabul. We constrain the ages of offset alluvial fans based on 10Be terrestrial cosmogenic nuclides (TCN) dating of well-embedded quartzite sandstone boulders and cobbles. The Ghat Bandakul alluvial fans are offset at 165 ± 15 m and 235 ± 24 m, for which 10Be TCN model ages average 46.9 ± 3.5 kyr and 66.6 ± 4.9 kyr, respectively, yielding a slip rate of 3.5 ± 0.4 mm/yr. At the Azadkhail site, we identified two offset terraces. Based on 500 ± 50 m offset of a geomorphic surface with 111.2 ± 10.5 kyr age, we obtain a slip rate of 4.5 ± 0.6 mm/yr. Combining the 800 ± 70 m left-lateral offset matching with an average age of 176.8 ± 17.1 kyr for the fan yields the same geomorphic slip rate of 4.5 ± 0.6 mm/yr. These slip rates are considerably lower than geologically, geomorphologically, and geodetically defined slip rates previously obtained along the southern Chaman fault. These results show a clear trend of decreasing fault slip rate with increasing distance to the northeast. The observations suggest that the southern portion of the fault accommodates most of the fault-parallel component of relative motion between the Indian and Eurasian plates. The lower slip rate of the Chaman fault in Afghanistan may be explained by the transfer of the left-lateral shear onto the Gardez and Mokur faults that splay northward from the Chaman fault.

Simulating the near-field pulse-like ground motions of the Imperial Valley, California, earthquake

Long-period pulse-like ground motions in the near-field are likely to induce severe damage to large structures due to resonance at the natural frequencies of engineered construction. To investigate the origin and characteristics of large velocity pulses from the seismic source, this study identifies 14 stations with velocity pulses from 32 strong-motion seismographs located in the near-field of the Imperial Valley MW 6.5 earthquake. The pulse-like ground motions are simulated by a kinematic approach using a fourth-order accurate finite-difference method. The results show that the slip asperity in the northern part of the fault plane contributes more to large velocity pulses than the asperity that originates in the hypocentral zone. The two-sided pulses on the fault-normal component and the one-sided pulses on the fault-parallel component are mainly regulated by the fault rupture and slip directions, respectively. Compared with the pseudo-velocity response spectrum, the displacement response spectrum better captures the resonance effect of long-period pulse-like ground motion on large structures. The location of the maximum ground motion coincides with the surface projection area of the large asperity, and the amplitude and the attenuation rate of each horizontal component vary with increasing distance from the fault. The difference in the ground motion peaks on both sides of the fault implies that the fault-normal component is more sensitive to the fault dip angle than the fault-parallel component. We reproduce the pulse-like ground motions up to 1 Hz by fitting the simulated velocity time histories, response spectrum and ground motions to observed data. Using the pulse records of the Imperial Valley earthquake, the 1994 Northridge MW 6.7 earthquake, and the 1999 Chi-Chi MW 7.6 earthquake, we compare the effects of earthquake magnitude on peak value and distribution of large velocity pulses, in which a reasonable consistency can be observed. Our simulated results of near-field pulse-like ground motions are beneficial to clarify the pulse mechanism.

Numerical modelling of the near-field velocity pulse-like ground motions of the Northridge earthquake

The seismic records acquired during the 1994 MW6.7 Northridge earthquake provide important data for studying the pulse-like ground motions in the vicinity of reverse faults. We selected 106 horizontal records from 468 strong ground motion records in the near-field region and rotated the original records into fault-parallel and fault-normal orientations. Large velocity pulses were simulated by the 3D finite difference method using a kinematic source model and a velocity structure model. Regression analysis was performed on the simulated and observed amplitudes of the velocity time history and response spectrum using the least-squares method. Our results show that the released energy and rupture time of asperities in the source model have important effects on the near-field velocity pulses, and the asperity near the initial rupture contributes more to the velocity pulses than does the asperity near the central region. The unidirectional and bidirectional characteristics of large velocity pulses are related to the thrust slip and rupture direction of the fault. The pulse period and the characteristic period are positively correlated with the rise time, and the pulse peak is regulated by multiple parameters of the subfaults. The distributions of the simulated PGV and Arias intensity agree well with the observed records, in which the contours exhibit asymmetric distribution and irregular elliptical attenuation in the near-field region, and the distributions exhibit a significant directivity along the fault. Moreover, the attenuation rate decreases with increasing distance from the fault. In addition, the fault-normal component is larger than that on the fault-parallel component, and the former decays faster. Velocity pulses larger than 30 cm/s are most likely to be distributed within approximately 15 km from the fault plane of the Northridge earthquake. Thus, the revealed pattern of the near-field velocity pulse-like ground motions indicates their close relation with the most severe earthquake effects.

Active structural control via metaheuristic algorithmsconsidering soil-structure interaction

In this study, multi-story structures are actively controlled using metaheuristic algorithms. The soil conditions such as dense, normal and soft soil are considered under near-fault ground motions consisting of two types of impulsive motions called directivity effect (fault normal component) and the flint step (fault parallel component). In the active tendon-controlled structure, Proportional–Integral–Derivative (PID) type controller optimized by the proposed algorithms was used to achieve a control signal and to produce a corresponding control force. As the novelty of the study, the parameters of PID controller were determined by different metaheuristic algorithms to find the best one for seismic structures. These algorithms are flower pollination algorithm (FPA), teaching learning based optimization (TLBO) and Jaya Algorithm (JA). Furthermore, since the influence of time delay on the structural responses is an important issue for active control systems, it should be considered in the optimization process and time domain analyses. The proposed method was applied for a 15-story structural model and the feasible results were found by limiting the maximum control force for the near-fault records defined in FEMA P-695. Finally, it was determined that the active control using metaheuristic algorithms optimally reduced the structural responses and can be applied for the buildings with the soil-structure interaction (SSI).

Near-Source Strong Pulses During Two Large MJMA 6.5 and MJMA 7.3 Events in the 2016 Kumamoto, Japan, Earthquakes

Extremely large ground motions with strong pulses were observed near source faults during two large MJMA 6.5 and MJMA 7.3 events of the 2016 Kumamoto earthquakes in Japan. To investigate the mechanisms for generation of near-source strong pulses during both events, we first performed strong ground motion simulations in a broadband frequency range between 0.2 and 10 Hz using the empirical Green’s function method. For both the M6.5 and M7.3 events, strong motion generation area (SMGA) source models were prepared to simulate the ground motions, which were able to reproduce well the characteristics of the observed ground motions in and around the source areas. We also conducted ground motion simulations based on hypothetical simple source models to study the effect of rupture directivity on near-source strong ground motions. The principal findings regarding rupture directivity effects on near-source strong ground motions are as follows: (1) During the M6.5 event, the forward and upward rupture directivities from two strike-slip SMGAs caused two distinct strong pulses in the fault normal and parallel components, respectively. (2) During the M7.3 event, the upward rupture directivity along the fault dip direction from the strike-slip SMGA, including a small normal-slip, caused a strong pulse in both the fault parallel and normal components.

Polarization of Near-fault Long-period Ground Motion

Through the analysis of typical near-fault ground motion, the inhomogeneity of the spatial distribution of long-period ground motion intensity on the fault parallel component (FP) and normal component (FN) is revealed. The study shows that the intensity of long-period ground motion on the fault parallel component is higher than that of on the fault normal component. This may be due to the fact that the velocity pulse is more easily formed on the fault parallel component higher than that of on the fault normal component, and the velocity pulse is more intense. The study is of great significance to the establishment of the attenuation relationship of near-fault ground motion and the seismic fortification of near fault structures.

Evaluation of the Strong Ground Motions in the Area Close to the Surface Faults

In Japan, the seismic waves radiated from the fault in the surface layers above the seismogenic layer are not considered in the usual strong motion prediction. However, in the inland crustal earthquakes, the strong ground motions in the areas close to the surface faults could be influenced by the seismic waves radiated from the fault in the surface layers. Hence, we evaluated the seismic waves radiated from vertical strike-slip and dipping reverse faults in the surface layers to investigate their influence on the strong motions. The results of the strike-slip fault showed that the seismic waves of the fault normal (FN) component were larger than those of the fault parallel (FP) component in the period range of 0.5–5 s. At least, 80–90% of the FN component was attributed to the seismic wave radiated from the fault in the seismogenic layer. Almost 100% of the FP component was attributed to the seismic waves radiated from the fault in the surface layers. On the other hand, the results of the reverse fault showed that the seismic waves were not attributed to those from the fault in the surface layers.

Source Modeling for Predicting Ground Motions and Permanent Displacements Very Close to the Fault Trace

A conventional “recipe” for strong ground motion prediction has been applied to the seismic fault (deep fault; located within seismogenic layer). In order to perform assessments of strong ground motions and permanent displacements at sites very close to the fault trace, we proposed the method of modeling that takes the entire ruptured fault from the ground surface to the seismic fault into account. Our approach was validated by the simulation of observed records obtained at stations very close to the fault trace of the mainshock of the 2016 Kumamoto Japan, earthquake (Mw7.1). Also, through the ground motion assessment performed for a hypothetical strike-slip fault with a 90[Formula: see text] dip angle, we found that adding the shallow fault had virtually no effect on acceleration time history, but it had a clear effect on the fault-parallel component of velocity and displacement time histories in the area close to the fault trace.

A new methodology for energy-based seismic design of steel moment frames

A procedure is proposed whereby input and hysteretic energy spectra developed for single-degree-of-freedom (SDOF) systems are applied to multi-degree-of-freedom (MDOF) steel moment resisting frames. The proposed procedure is verified using four frames, viz., frame with three-, five-, seven- and nine-stories, each of which is subjected to the fault-normal and fault-parallel components of three actual earthquakes. A very good estimate for the three- and five-story frames, and a reasonably acceptable estimate for the seven-, and nine-story frames, have been obtained. A method for distributing the hysteretic energy over the frame height is also proposed. This distribution scheme allows for the determination of the energy demand component of a proposed energy-based seismic design (EBSD) procedure for each story. To address the capacity component of EBSD, a story-wise optimization design procedure is developed by utilizing the energy dissipating capacity from plastic hinge formation/rotation for these moment frames. The proposed EBSD procedure is demonstrated in the design of a three-story one-bay steel moment frame.

The 3D numerical simulation of near-source ground motion during the Marsica earthquake, central Italy, 100 years later

In this paper we show 3D physics-based numerical simulations of ground motion during one of the most devastating earthquakes in the recent Italian history, occurred on Jan 13, 1915, Marsica, Central Italy. The results provide a realistic estimate of the earthquake ground motion and fit reasonably well both the geodetic measurements of permanent ground settlement, and the observed macroseismic distribution of damage. In addition, these results provide a very useful benchmark to improve the current knowledge of near-source earthquake ground motion, including evaluation of the best distance metrics to describe the spatial variability of the peak values of ground motion, the relative importance of fault normal vs fault parallel components, the conditions under which vertical ground motion may prevail, as well as the adequacy of 1D vs 3D modelling of site amplification effects.

Analysis of Strong Ground Motion Characterization in the 2013 Lushan Earthquake

Lushan earthquake on 20th April, 2013 was another thrust fault earthquake occurred at Longmen Mountain Fault Zone after 2008 Wenchuan Ms8.0 earthquake. Based on ground motion attenuation model, this paper has chosen 45 strong motion records with rupture distance less than 200km, to analyze the hanging wall effect, topographic effect and rupture directivity effect of Lushan earthquake. The results show that hanging wall effect in Lushan earthquake was not obvious as 2008 Wenchuan earthquake; ground motion in mountain areas attenuated with increasing rupture distance more quickly than that in plain areas; rupture directivity effect is obvious for two components of horizontal ground motion, which are fault-perpendicular and fault-parallel components. PGA in the forward rupture area is larger than those in the backward rupture area. With the period increased, the gap between backward and forward rupture area become small, and finally PGD in backward rupture area is greater than those in the forward rupture area.

Effect of seismic super-shear rupture on the directivity of ground motion acceleration

The effect of seismic super-shear rupture on the directivity of ground motions using simulated accelerations of a vertical strike-slip fault model is the topic of this study. The discrete wave number/finite element method was adopted to calculate the ground motion in the horizontal layered half space. An analysis of peak ground acceleration (PGA) indicates that similar to the sub-shear situation, directivity also exists in the super-shear situation. However, there are some differences as follows: (1) The PGA of the fault-normal component decreases with super-shear velocity, and the areas that were significantly affected by directivity in the PGA field changed from a cone-shaped region in the forward direction in a sub-shear situation to a limited near-fault region in a super-shear situation. (2) The PGA of the fault-parallel and vertical component is not as sensitive as the fault-normal component to the increasing super-shear velocity. (3) The PGA of the fault-normal component is not always greater than the fault-parallel component when the rupture velocity exceeds the shear wave velocity.

Proposed modification on velocity attenuation relationships in West of with special respect to Dorood fault

As a routine procedure, the estimation of source parameters such as focal mechanism and magnitude is known for moderate to great earthquakes, however some of them such as directivity effect and filing step are rarely taking into account. According to the radiation pattern, directivity effect is a source parameter, which causes significant spatial variations in near field strong ground motion. Its significant variations could be obtained on strike normal component of velocity in forward and backward directions. This study has an attempt on estimation of a modification factor, which can define the effect of directivity in empirical attenuation relationships in Dorood fault. In order to model unilateral and bila- teral rupturing Finite Elements Method (FEM) is applied to achieve reliable functions.The authors used Somervill et al. (1997) directivity model parameter with some changes as variable parameter. To obtain modified ground motion parame- ters, these models were applied for earthquakes which Dorood fault caused them. These parameters consist of fault normal component to fault parallel component of velocity ratio ( Vn/Vp ) and fault normal component to average horizontal veloc- ity ratio (Vn/V ). It shows Vn/V is controlled by directivity angle, distance between the site, epicenter and rupture length. This ratio has the same trend in studied region earthquakes velocity data.