Near-field Strong Ground Motion Research Articles

Accessing Near-Field Strong Ground Motions Using a Multi-Scheme Method in the Kalawenguquan Fault, Xinjiang, China

The middle segment of the Kalawenguquan fault has been active since the Holocene, with a maximum credible earthquake magnitude of MS 7.5. We established two source models based on empirical relationships, as well as geological, geomorphological, and seismic characteristics. Taking into account the uncertainties of simulation parameters, we adopted the stochastic finite-fault method to calculate all combinations of a multi-scheme simulation. The effects of different source models, initial rupture points, and site locations on the prediction of ground motion parameters were analyzed. The results indicate that when a site is located on a smaller asperity and is a certain distance from the largest asperity, the simulation results are higher. For different sites, when the initial rupture point is located near the smaller rather than the larger asperity, the acceleration response spectra are higher. Our results show that the relationships between the initial rupture points, asperities, and sites have a significant impact on the simulation results. Therefore, our study highlights the relevance of determining the initial rupture point and source model to obtain a reasonable evaluation for near-field strong ground motion simulations at major infrastructures.

Predominant Frequency in Near-Field Strong Ground Motion by Analysis of Displacement Response Spectra

A literature review on the spectral content of seismic ground motion indicates that a clear predominant frequency in earthquakes is very difficult to define. Here, it is considered that this has been so because the usual seismic record or response quantity is always employed: acceleration. In this work, an attempt is made to define a single predominant frequency for strong seismic ground motion in the near field with a different idea. It is considered that this is possible if the concentration is on displacement rather than on ordinary acceleration. In particular, relative displacement response spectra will be studied, instead of the common acceleration one, and the existence of clear and neat maximum spectral displacements around, statistically, a single and general proposed predominant frequency will be investigated for a set of twenty very strong (magnitude larger than 6.5 MW) world events.

Assessment of Near-Field Strong Ground Motion Effects on Offshore Wind Turbines Resting on Liquefiable Soils Using Fully Coupled Nonlinear Dynamic Analysis

Assessment of Near-Field Strong Ground Motion Effects on Offshore Wind Turbines Resting on Liquefiable Soils Using Fully Coupled Nonlinear Dynamic Analysis

Resilient clevis-based connections equipped with hybrid Ni–Ti shape memory alloys and steel tendons: Experimental and FE investigations

Shape memory alloys (SMAs) are a group of novel materials capable of withstanding large deformations and returning to their initial state using specific mechanisms. This unique capability has led to their increasing use in various engineering fields, especially in engineered structures, to maximize the recentering capability and minimize the residual deformations under dynamic loadings. Despite having the ability to withstand large deformations without being ruptured or damaged, these materials have moderate energy absorption and dissipation capacity. Therefore, this study examines the behavior of a novel type of clevis-based beam-to-column connection, which is categorized as a semi-rigid joint and is made of a combination of SMA and steel tendons using experimental and numerical investigations. The reason for combining steel tendons with SMA tendons is to investigate the influence of increasing energy absorption capability and reducing permanent deformation of the connection. The connection is made by incorporating steel tendons and SMA tendons, each in two different sizes, with varying arrangements under four different cyclic loading protocols, representing far- and near-field strong ground motions. From a total of 24 experiments and subsequent numerical investigations, it was observed that the proposed connection has an excellent recentering capability with a maximum of 0.004 (radian) recoverable deformation and large energy dissipation capacity with equivalent viscous damping of up to 35% after being subjected to cycles up to 6% drift. In contrast, tendons have improved its overall resilience and behavioral characteristics. • Twenty-four clevis-based connections with shape memory alloy and steel tendons were tested. • Testings were conducted under various loading protocols representing far- and near-fault ground motions. • The connection specimens have good recentring capabilities. • Suitable energy dissipation capability was observed for the specimens. • The equivalent viscous damping of up to 30% was recorded.

Simulation of Dynamic Rupture Process and Near-Field Strong Ground Motion for the Wenchuan Earthquake

ABSTRACT The 2008 Wenchuan earthquake that occurred in the Longmenshan thrust zone is the most serious natural disaster recorded in China’s densely populated areas over the past few decades. Its northeast-trending principal fault—the Yingxiu–Beichuan fault (YXBCF), has a complex, segmentary-cascaded geometry and was dominated by the thrust slip in the southwest section, while the right-lateral slip in the northeast section. Some previous works believe that there may have occurred a supershear rupture in the strike-slip-dominated northeast section. Here we revisited this earthquake by exploring the dynamic rupture mechanism of the principal fault and showed a hypothetical scenario with supershear rupture occurring in its northeast section. We utilized a 3D curve grid finite-difference method to simulate the spontaneous rupture process of the YXBCF and corresponding near-field strong ground motion. An appropriate focal process is obtained using the trial-and-error method within reasonable parameters, and its related responses are validated by geological investigations and geophysical inversions. Besides, a large hypothetical oblique propagating supershear rupture is shown between Beichuan and Nanba in the northeast section of the YXBCF. Its transition mechanism is related to the Gaochuan–Beichuan conjugated fault from the fault geometry perspective, and belongs to the joint action of fault barrier and free surface. Such a supershear scenario is not rejected by observations and could increase the credibility of the occurrence of supershear rupture in the northeast section of the YXBCF during the Wenchuan earthquake.

Strong Ground Motion Recorded by High-Rate GPS during the 2021 Ms 6.4 Yangbi, China, Earthquake

Abstract The 2021 Ms 6.4 Yangbi earthquake, Yunnan, China, was recorded by the Dali Global Positioning System (GPS) network comprising 37 permanent stations within 100 km of the epicenter. All of these GPS stations recorded 1 Hz data, and 12 of them also recorded 5 Hz data. Using sophisticated data processing strategies, especially the method to overcome ionospheric and multipath errors, near-field waveforms of epoch-by-epoch displacement of all of the GPS stations within an epicentral distance of ∼50 km were derived from high-rate GPS observations with a root mean square error of 3.8, 4.2, and 8.2 mm for the east–west, north–south, and up components, respectively. The peak ground displacement of up to 14 cm in the horizontal direction and 4.2 cm in the vertical direction and the largest coseismic displacement of 3.1 cm in the horizontal direction and 3.2 cm in the vertical direction were observed for the stations within 6–9 km of the epicenter. The waveforms, with dominant periods between 7 and 10 s, present a systematic change in shape as a function of distance from the source, which demonstrates that the high-rate GPS observations can provide reliable relative-displacement response spectra at the periods needed in the design of large structures for resisting strong earthquakes. Comparisons of the GPS displacement time series at 1, 2.5, and 5 Hz suggest that 5 Hz data are able to capture strong ground information that are of interest to both earthquake seismologists and engineers. We conclude that the displacement waveforms and motion trajectories from high-rate GPS observations provide unique additional information of the near-field strong ground motion that is valuable to seismologists in unraveling the dynamic process of fault rupture and to engineers for designing large structures with very long period response.

Evaluation of horizontal ground motion waveforms at Sedongpu Glacier during the 2017 M6.9 Mainling earthquake based on the equivalent Green's function

The terrain along the Tibet Railway is primarily steep mountains and valleys with complex geological structures. The occurrence of the Mainling earthquake indicates that the intensity of seismicity in the eastern structural junction area has strengthened, and the potential risk of earthquake-induced disasters such as landslides and debris flows is also increasing. The earthquake engineering community generally recognizes that the prediction of near-field strong ground motion can reduce the disasters caused by future large earthquakes and can guide earthquake prevention, disaster reduction and seismic design along the Sichuan–Tibet railway. The M6.9 Mainling earthquake affected the stability of Sedongpu Glacier near the epicentre. A glacier avalanche occurred under the coupling of multiple factors, including post-earthquake and precipitation events. The waveform and response spectra of a strong earthquake are key input parameters for investigating the seismic triggering mechanisms of landslides and glacier avalanches and accurately reproducing the dynamics of such disasters. In this paper, the concept of the equivalent Green's function is introduced, and various source parameter uncertainties are fully considered. The waveform and response spectra of the Mainling earthquake at Sedongpu Glacier are simulated, and the most likely seismic waveform is comprehensively assessed from multiple perspectives. This work can provide reliable acceleration waveform input for the analysis of ground motion damage and the study of earthquake-induced disaster mechanisms at important locations along the Sichuan–Tibet railway and provide a scientific reference for earthquake prevention and disaster reduction along the railway.

Effect of Foundation Flexibility on the Seismic Performance of a High-Rise Structure under Far-Field and Near-Field Earthquakes

In this study, the seismic performance of a 20-storey steel structure with a mat foundation located on layered soil is investigated under an array of strong ground excitations, which includes 6 far-fault and 6 near-fault earthquakes. Eight different modes for soil layering have been considered in the numerical simulation. FLAC 2D nonlinear platform has been used to model the near-realistic behavior. To this end, hundred lines of codes and sub-routines have been developed in this platform to perform the analysis. The results of the analyzes include the absolute displacement of the floors, the ratio of the relative displacement of the floors, the shear force, the axial force, and the bending moment of the columns. It was concluded that for a 20-story structure on a mat foundation under both far-field and near-field earthquakes, the most reliable type of soil is the dense sandy soil and the most critical case is the soft clay soil. It was also observed that the near-field strong ground motions have imposed more critical structural responses compared to far-field records.

Predicting the near-field strong ground motion based on uncertainties in asperities: an opportunity to reproduce the characteristics of the 1970 Tonghai earthquake (Ms 7.8)

Studying and understanding the characteristic ground motions of destructive earthquakes is very important in the prevention of earthquake disasters. In this paper, two 2018 Ms 5.0 earthquakes are used as an empirical Green’s function to reproduce the ground motion strength of the 1970 Ms 7.8 Tonghai earthquake. The present paper considers the uncertainties in the numerical simulation, the source model, the asperities, and the initial rupture positions. The obtained peak ground acceleration (PGA), the time history of the acceleration, and the acceleration response spectrum at each station are compared with the ground motion strength at corresponding stations for the Ms 8.0 Wenchuan earthquake to test the reliability of the ground motion simulation. The results show that the PGA of the one-asperity source model is the largest. With an increasing number of asperities, the ground motion strength decreases, and the earthquake duration increases, indicating that an increase in the number of asperities disperses seismic energy. The two-asperity source model is consistent with the real source model of the Tonghai earthquake. The acceleration time history and acceleration response spectrum at each station reflect the characteristics of the ground motion strength of the destructive Tonghai Ms 7.8 earthquake. Thus, reproducing the main ground motion strength characteristics of the Tonghai earthquake by combining the empirical Green's function method with two Ms 5.0 earthquakes is feasible.

Predicting Near-Field Strong Ground Motion of the Huaxian Ms8.5 Earthquake Based on Uncertainty Factors of Asperities

The Weihe Plain is at high risk of disastrous earthquakes, such as the Huaxian Ms8.5 earthquake, which caused enormous casualties and economic losses. Therefore, reproducing the strong ground motion characteristics of the Huaxian earthquake is important for seismic design and disaster mitigation. The empirical Green’s function method is used to predict the ground motion characteristics of the Huaxian Ms8.5 earthquake by considering the uncertainty factors of asperities, considering the limited observations in the Weihe Plain and the inaccessibility of the Earth’s interior. The uncertainty asperity factors can be studied by the logic tree method, and source models considering these factors are constructed here. The uncertainty factors include the seismic moment M0, number of subfaults N, stress drop of an asperity Δσ, and asperity area Sa. The asperity area is assigned values of 19%, 22%, and 25% of the fault rupture area; the M0 values of the corresponding asperities account for 40%, 44%, and 48% of the entire M0; and there are two to four asperities. The permutations are combined into multiple-asperity source models. The two-asperity source models reflect the Huaxian earthquake characteristics better than the three- or four-asperity models. The asperity area accounts for approximately 22–25% of the fault rupture area, while the M0 of the corresponding asperities accounts for 44% and 48% of the entire M0. The long-axis direction of the ground motion distribution is the same as that of the mountains southeast of the Weihe Plain. The azimuth angle of the elliptical long axis is approximately 40–60° northeast. The greater the magnitude is, the more complex the number, location, and area of the asperities. This research extends the application of the empirical Green’s function method and can numerically simulate seismic intensity characteristics in areas with destructive earthquakes but few seismic records.

Near-Field Strong Ground Motions from GPS-Derived Velocities for 2020 Intermountain Western United States Earthquakes

Abstract In early 2020, four moderate sized earthquakes occurred in the Intermountain region of the western United States, two M 6.5 events in Challis, Idaho, and Monte Cristo Range, Nevada; an M 5.7 in Magna, Utah, within the Salt Lake City metropolitan area; and an M 5.8 in the Owens Valley of California. Although the Magna and Owens Valley earthquakes were well recorded in the near field with an array of seismic instrumentation, the Challis and Monte Cristo events were not densely recorded. All of the events, however, have reasonable coverage with high rate Global Positioning System (GPS) stations in the near field. Here, I report on strong-motion observations recorded at 19 regional GPS stations at 5 Hz. I compare these observations with seismic recordings where available and ShakeMap estimations of peak ground velocity to find good agreement with a natural-log residual of ±0.5. Furthermore, I compute the correlation between collocated stations and show a strong positive correlation >0.65. This study highlights the utility of high-rate GPS velocity observations to strong-motion seismology.

Effects of Near-fault Strong Ground Motions on Probabilistic Structural Seismic-induced Damages

Seismic fragility curves measure induced levels of structural damage against strong ground motions of earthquakes, probabilistically. These curves play an important role in seismic performance assessment, seismic risk analysis and making rational decisions regarding seismic risk management of structures. It has been demonstrated that the calculated fragility curves of structures are changed while the structures are excited by near-field strong ground motions in comparison with far-field ones. The objective of this paper is to evaluate the extents of modification for various performance levels and variety of structural heights. To achieve this goal, Incremental Dynamic Analysis (IDA) method is applied to calculate seismic fragility curves. To investigate the effects of earthquake characteristics, two categories of strong ground motions are assumed through IDA method, i.e. near and far-field sets. To study the extent of modification for various heights of structures, 4 – 6 and 10 stories moment-resisting concrete frames are considered as case studies. Furthermore, to study the importance of involving near-field strong ground motions in seismic performance assessment of structures, the damage levels are considered as the renowned structural performance levels (i.e. Immediate Occupancy, Life Safety, Collapse Prevention and Sidesway Collapse). Achieved results show that the fragility curve of low-rise frame (i.e. 4-story case study) for IO limit state presents more probability of damage applying near-fault sets in comparison with far-fault set. Investigating fragility curves of the other performance levels (i.e. LS, CP and Collapse) and the higher frames, a straightforward conclusion, regarding probability of damage. To achieve the rational results for the higher frames, mean annual frequency of exceedance (MAFE) and probability of exceeding limit states in 50 years are calculated. MAFE is defined as the integration of structural fragility curve over seismic hazard curve. According to the achieved results for 6-story frame, if the structure is excited by near-field strong ground motions the probability of exceedance for LS, CP and collapse limit states in 50 years will be increased up to 11%, 2.4%, 0.7% and 0.4% respectively, comparing with the calculated probabilities while far-field strong ground motions are applied. On the other hand, while the 10-story case study is excited by near-field strong ground motions, the exceedance probability values for mentioned limit states decreases up to 20%, 5%, 4% and 4%, respectively. Consequently, it can be concluded that the lower is the height of the structure, the more will be the increment of probability of damage in the near-field conditions. Furthermore, this increment is much more for IO limit state in comparison with other limit states. These facts can be applied as a precaution for seismic design of low-rise structures, while they are located at the vicinity of active faults.

Sensitivity analysis study of the source parameter uncertainty factors for predicting near-field strong ground motion

Uncertainty factors have substantial influences on the numerical simulations of earthquakes. However, most simulation methods are deterministic and do not sufficiently consider those uncertainty factors. A good approach for predicting future destructive earthquakes that is also applied to probabilistic hazard analysis is studying those uncertainty factors, which is very significant for improving the reliability and accuracy of ground-motion predictions. In this paper, we investigated several uncertainty factors, namely the initial rupture point, stress drop, and number of sub-faults, all of which display substantial influences on ground-motion predictions, via sensitivity analysis. The associated uncertainties are derived by considering the uncertainties in the parameter values, as those uncertainties are associated with the ground motion itself. A sensitivity analysis confirms which uncertainty factors have large influences on ground motion predictions, based upon which we can allocate appropriate weights to those uncertainty factors during the prediction process. We employ the empirical Green function method as a numerical simulation tool. The effectiveness of this method has been previously validated, especially in areas with sufficient earthquake record data such as Japan, Southwest China, and Taiwan, China. Accordingly, we analyse the sensitivities of the uncertainty factors during a prediction of strong ground motion using the empirical Green function method. We consequently draw the following conclusions. (1) The stress drop has the largest influence on ground-motion predictions. The discrepancy between the maximum and minimum PGA among three different stations is very large. In addition, the PGV and PGD also change drastically. The Arias intensity increases exponentially with an increase in the stress drop ratio of two earthquakes. (2) The number of sub-faults also has a large influence on various ground-motion parameters but a small influence on the Fourier spectrum and response spectrum. (3) The initial rupture point largely influences the PGA and Arias intensity. We will accordingly pay additional attention to these uncertainty factors when we conduct ground-motion predictions in the future.

On Estimation of Seismic Residual Displacements in Reinforced Concrete Single-Column Bridges Through Force–Displacement Method

Bridges normally undergo nonlinear deformations during a near-field strong ground motion resulting in a critical deviation of their columns from the plumb state due to considerable residual deformations. The conventional hysteresis models formulated for typical concrete columns are normally used for this purpose which most of times fail to correctly predict the residual deformations occurred as a result of a one-sided or directivity pulse excitation. The present research aims at development of a peak-oriented hysteresis model being able to regenerate residual deformations more reasonable compared with the conventional hysteresis models. This multi-linear peak-oriented model considers strength deterioration in each half cycle in addition to stiffness degradations in unloading cycles. Yielding points differ in both positive and negative sides of the hysteresis model that enables us to define a different elastic stiffness of both sides in asymmetric concrete sections. This work also compares the obtained results to the conventional hysteresis models, namely bilinear, Clough, Q-Hyst, Takeda, and Bouc-Wen in terms of prediction of residual nonlinear deformations in cyclic analysis or dynamic analysis of reinforced concrete single-column bridge piers. The obtained results prove higher relative accuracy of the proposed model.

Seismic vulnerability assessment and risk modelling of telecommunication systems

Lessons learned from past earthquakes have shown that continued operation of urban lifeline systems during the emergency can facilitate better relief and operation activities and reduce casualties and economic losses. A telecommunication system is one of the most important parts of an urban lifeline and plays a vital role in risk management. The primary goal of this paper is to assess the seismic vulnerability of these systems by developing vulnerability curves and comparing the effects of the near and far-field earthquakes on the curves. Two sets of seven near-field and far-field strong ground motion records have been analysed and vulnerability curves have been derived. The results are compared with HAZUS vulnerability curves. An exceedance probability curve is developed for a city in southern Iran as a case study, using seismic hazard curves and probabilistic earthquake risk modelling.

Strong motion characteristics of the M w 6.6 Lushan earthquake, Sichuan, China — an insight into the spatial difference of a typical thrust fault earthquake

Near-field strong ground motions are useful for engineering seismology studies and seismic design, but dense observation networks of damaging earthquakes are still rare. In this study, based on the strong-motion data from the M w 6.6 Lushan earthquake, the ground motion parameters in different spatial regions are systematically analyzed, and the contributions from different effects, like the hanging-wall effect, directivity effect, and attenuation effect are separated to the extent possible. Different engineering parameters from the observed ground motions are compared with the local design response spectra and a new attenuation relation of Western China. General results indicate that the high frequency ground motion, like the peak ground acceleration, on two sides of the fault plane is sensitive to the hanging-wall effect, whereas the low frequency ground motion, like the long period spectral acceleration, in the rupture propagation direction is affected by the directivity effect. Moreover, although the M w 6.6 Lushan earthquake is not a large magnitude event, the spatial difference of ground motion is still obvious; thus, for a thrust faulting earthquake, in addition to the hanging effect, the directivity effect should also be considered.

An Improved Stochastic Finite-Fault Method Based on Energy

Owing to the simulated ground motion energy distribution by stochastic finite-fault method is not reasonable, near-field bedrock strong ground motion acceleration time histories are used to study. Fourier transform is adapted to analysis the variation of the energy accumulation curve with frequency. The results show that the record energy accumulation curve is a steep rise curve, 80% of total energy of the vertical ground motion is concentrated on the 2.5-15Hz, while the horizontal is mainly concentrated on the 2-11Hz. An improved stochastic finite-fault method is proposed by multiplying an amplification factor in some frequency. The results show that multiplying an amplification factor, the simulated acceleration energy accumulation curve matches to the record acceleration energy accumulation curve, and the peak of simulated acceleration response spectrum tends to the record acceleration value.

An Improved Source Model for Simulation Near-Field Strong Ground Motion Acceleration Time History

The key to near-field strong ground motion simulation based on stochastic finite fault method is to determine the spectrum of ground motion. We present an improved source spectrum model for simulation near-field strong ground motion acceleration time history. We combine Masudas source spectrum model with scaling factor Hij to keep radiation energy conservation and reflect the energy decrease with frequency at low to mid frequencies. We calculate the Fourier amplitude spectrum Fa, accelerate response spectrum Sa, velocity response spectrum Sv and displacement response spectrum Sd of simulation time histories. By comparative analysis of the laws of spectrum values (Fa, Sa, Sv, Sd) with the variation of frequency or period, we discusses the effects of sub-fault dividing scheme, the method of determining scale factor and source spectrum model on spectrum values (Fa, Sa, Sv, Sd). The results show that sub-fault dividing scheme has slightly effect on the model presented in this paper, and the model enable to reflect the sink laws of source spectrum value in mid-to-low frequencies well. We demonstrate that the improved model is superior to other commonly used models.

Using a Lumped Mass, Nonuniform Stiffness Beam Model to Obtain the Interstory Drift Spectra

AbstractThe drift spectrum has recently been introduced as a new measure for estimating the interstory drift demands in buildings under near-field earthquakes. In this study, a method for estimating the drift demands in buildings with different structural systems is presented. Unlike previous studies that use a continuous beam, a stick model is employed to estimate the seismic-induced interstory drift demands. The proposed method can overcome the deficiencies of the previously introduced models. It considers the effect of heightwise stiffness reduction on drift demands, which is shown to be very important, and makes it possible to construct the drift spectra for low and medium-rise as well as high-rise buildings. The suggested method is simple because it uses the well-established modal analysis technique of lumped mass beams. The drift spectra for shear building models are constructed using near-field strong ground motions. The effects of the ratio of the lateral stiffness of top story to that of first st...

Elastic floor response spectra of nonlinear frame structures subjected to forward-directivity pulses of near-fault records

This article presents the statistical characteristics of elastic floor acceleration spectra that represent the peak response demand of non-structural components attached to a nonlinear supporting frame. For this purpose, a set of stiff and flexible general moment resisting frames with periods of 0.3-3.6 sec. are analyzed using forty-nine near-field strong ground motion records. Peak accelerations are derived for each single degree of freedom non-structural component, supported by the above mentioned frames, through a direct-integration time-history analysis. These accelerations are obtained by Floor Acceleration Response Spectrum (FARS) method. They are statistically analyzed in the next step to achieve a better understanding of their height-wise distributions. The factors that affect FARS values are found in the relevant state of the art. Here, they are summarized to evaluate the amplification and/or reduction of FARS values especially when the supporting structures undergo inelastic behavior. The properties of FARS values are studied in three regions: long-period, fundamental-period and short-period. Maximum elastic acceleration response of non-structural component, mounted on inelastic frames, depends on the following factors: inelasticity intensity and modal periods of supporting structure; natural period, damping ratio and location of non-structural component. The FARS values, corresponded to the modal periods of supporting structure, are strongly reduced beyond elastic domain. However, they could be amplified in the transferring period domain between the mentioned modal periods. In the next step, the amplification and/or reduction of FARS values, caused by inelastic behavior of supporting structure, are calculated. A parameter called the response acceleration reduction factor (<TEX>$R_{acc}$</TEX>), has been previously used for far-field earthquakes. The feasibility of extending this parameter for near-field motions is focused here, suggested repeatedly in the relevant sources. The nonlinearity of supporting structure is included in (<TEX>$R_{acc}$</TEX>) for better estimation of maximum non-structural component absolute acceleration demand, which is ordinarily neglected in the seismic design provisions.