Near-fault Strong Ground Motions Research Articles

Numerical Investigation on Sloshing Phenomena in U-Shaped Containers Subjected to Near-Fault Strong Ground Motions

In a laterally excited, partially liquid-filled U-shaped container, oscillation is the predominant motion of the liquid. However, there would be some sloshing in the liquid free surface at the vertical limbs of the container. Due to the presence of high-energy velocity pulses, near-fault ground motions can cause significant sloshing in the vertical limbs of the container. Thus, it is necessary to examine the effect of near-fault earthquake excitations on the sloshing liquid height, sloshing-induced hydrodynamic pressure, and shear stress at the walls of the U-shaped containers. The same is attempted in this paper. The standard “k-epsilon” turbulence model with enhanced wall function is considered in this study. The outcome of this study reveals that the time-wise frequency variation of the near-fault ground motions significantly affects the sloshing response of the liquid stored in the U-shaped containers. It is observed that the sloshing-induced hydrodynamic pressure is severely influenced by the frequency content of the ground motion records rather than their peak ground acceleration.

Parameter estimation for predicting near-fault strong ground motion and its application to Lushan earthquake in China

Stochastic finite-fault modelling based on the dynamic corner frequency is a widespread method for synthesizing near-fault ground motions at high frequencies and has been proven to be an effective tool for simulating high-frequency ground motions by researchers globally. Many input parameters, which have more uncertain effects on the synthetic result, are related to sources, sites, and paths in stochastic modelling. Thus, it is difficult to select reasonable parameters. When using the stochastic finite-fault method, the key link to be considered is how to determine the input parameters required for simulations. Based on this fact, this study analyzed and discussed the sensitivity of several important input parameters in the simulation parameters to the simulation results. The results showed that for the Class C site stations, the crustal and local site amplification factors must be considered simultaneously. Overall, the influence of the high-frequency attenuation parameter κ0 calculated using different methods on the simulation results is not evident. For near-fault stations, various upper-edge buried depth synthetic response spectra can be set, and finally, the average value is taken as the final synthetic recorded response spectra. When using the random source model, the rupture starting point must be set on the subfault in the middle along the fault length and width direction. The conclusions provide a basis for a highly reasonable and rapid determination of input parameters when using the stochastic finite-fault simulations for practical engineering applications and can improve the simulation accuracy to apply the finite source modelling to rebuild scenarios and evaluate and alleviate the seismic hazard in the target region.

The computation of strong ground motion for the near fault of the Kanding earthquake

In this study, the earthquake fault of the Kanding earthquake that occurred on November 22, 2014 is set as the target fault. Based on the Kanding earthquake fault geometry parameters and the technology of broadband simulation of ground motion, the near-fault strong ground motion of the Kangding earthquake is synthesized. Compared with the inversion achievements on the slip distribution of the Kangding earthquake fault, the slip distribution of the Kangding earthquake fault is first decided and selected. Using the representation theory of ground motion, the near-fault strong ground motion of the Kangding earthquake is then calculated. To validate the simulation method, the recordings at the strong motion stations and the simulation results on the location of the strong-motion stations are compared. Lastly, the spatial contour of the peak ground acceleration (PGA) and the peak ground velocity (PGV) in a region less than 100 km away from the epicenter of the Kangding earthquake are computed and analyzed. The results show some correlations between the amplitude of PGA, PGV, the spectral shapes of acceleration of the ground motion, and the slip distributions of the earthquake faults. For the ground motion stations with epicenter distances less than 50 km, the calculations of the ground motion velocity spectra shape is similar to those of the recordings except for the high-frequency components. For the ground motion stations with epicenter distances longer than 50 km, the calculations of the PGV amplitude at the strong ground motion station location are similar to the ground motion recordings. In general, the theoretical computation can ascertain the strong ground motion variation of the Kanding earthquake. Additionally, the correlations between the slip distributions of the Kanding fault and the ground PGA are analyzed, and the reasons why only minor damages were caused by the Kangding earthquake on the Kanding city are explained.

Disaster mechanism of Donghekou landslide in the Ms8.0 Wenchuan earthquake

During the “512” Wenchuan earthquake, Donghekou, which is located at the end of the seismogenic structure, experienced serious collapse and slide, resulting in serious disasters. In this paper, based on the analysis of near-fault strong ground motion records of Wenchuan earthquake, the collection of seismogenic structural data and near-fault structural damage data, the disaster mechanism of Donghekou landslide is studied. The earthquake damage of Donghekou was caused by pulse-like ground motion and the surface rupture along the seismogenic structure. The surface rupture at the far end of Donghekou participated in the formation of the pulse-like ground motion.

Inelastic displacement ratios for non-structural components in steel framed structures under forward-directivity near-fault strong-ground motion

This paper describes a detailed numerical investigation into the inelastic displacement ratios of non-structural components mounted within multi-storey steel framed buildings and subjected to ground motions with forward-directivity features which are typical of near-fault events. The study is carried out using detailed multi-degree-of-freedom models of 54 primary steel buildings with different structural characteristics. In conjunction with this, 80 secondary non-structural elements are modelled as single-degree-of-freedom systems and placed at every floor within the primary framed structures, then subsequently analysed through extensive dynamic analysis. The influence of ground motions with forward-directivity effects on the mean response of the inelastic displacement ratios of non-structural components are compared to the results obtained from a reference set of strong-ground motion records representing far-field events. It is shown that the mean demand under near-fault records can be over twice as large as that due to far-fault counterparts, particularly for non-structural components with periods of vibration lower than the fundamental period of the primary building. Based on the results, a prediction model for estimating the inelastic displacement ratios of non-structural components is calibrated for far-field records and near-fault records with directivity features. The model is valid for a wide range of secondary non-structural periods and primary building fundamental periods, as well as for various levels of inelasticity induced within the secondary non-structural elements.

Study on the disaster mechanism of near-fault pulse-like ground motion of M8.0 Wenchuan earthquake

With the improvement of observation quality, more and more near-fault strong earthquake records have been obtained. Through the analysis of near-fault strong ground motion records of Wenchuan earthquake, the collection and field investigation of seismogenic structural data, as well as the collection and field investigation of near-fault structural damage data, the disaster mechanism of Wenchuan earthquake is studied. The impulsive ground motion (directional effect, permanent displacement effect, etc.) near the fault is determined. It is confirmed that the pulse-like ground motion (directivity effect, permanent displacement effect, etc.) near-fault is the main cause of earthquake damage. Pulse-like ground motion has the characteristics of high peak value, wide frequency band and long duration. Therefore, it is easy to resonate with the structures with different basic periods, thus causing serious direct disasters and indirect secondary disasters.

Seismic risk analysis of concrete moment-resisting frames against near-fault earthquakes

Characteristics of earthquake strong ground motions play an important role in the calculation of seismic-induced risk imposed on the structures. Distinguished features exist in movements recorded near seismic sources, as a result of a substantial amount of energy in a short period of record arrival time. In this article, seismic risk analysis of concrete moment-resisting frames due to near-fault strong ground motion is calculated and compared with that of caused by far-field strong ground motions. To achieve this goal, three moment-resisting frames with 4, 6, and 10 stories were designed based on international seismic design code. These frames are modeled applying modified Ibarra–Krawinkler moment–rotation nonlinear model in which strength and stiffness deterioration are involved. Seismic risk analysis of the frames is implemented using the Pacific Earthquake Engineering Research Center approach. Through this approach, probabilistic seismic hazard, probabilistic structural demand, probabilistic structural damage, and probabilistic loss curves are combined. Mean annual frequency of exceedance of seismic-induced losses presents probabilistic seismic risk of the sampled frames. According to the achieved results, the four-story frame (representative of low-rise frames) is more prone to be affected by near-fault strong ground motions in view of calculated seismic-induced risks.

Evaluation of seismic performance of mid-rise reinforced concrete frames subjected to far-field and near-field ground motions

Damages to buildings affected by a near-fault strong ground motion are largely attributed to the vertical component of the earthquake resulting in column failures, which could lead to disproportionate building catastrophic collapse in a progressive fashion. Recently, considerable interests are awakening to study effects of earthquake vertical components on structural responses. In this study, detailed modeling and time-history analyses of a 12-story code-conforming reinforced concrete moment frame building carrying the gravity loads, and exposed to once only the horizontal component of, and second time simultaneously the horizontal and vertical components of an ensemble of far-field and near-field earthquakes are conducted. Structural responses inclusive of tension, compression and its fluctuations in columns, the ratio of shear demand to capacity in columns and peak mid-span moment demand in beams are compared with and without the presence of the vertical component of earthquake records. The influences of the existence of earthquake vertical component in both exterior and interior spans are separately studied. Thereafter, the correlation between the increase of demands induced by the vertical component of the earthquake and the ratio of a set of earthquake record characteristic parameters is investigated. It is shown that uplift initiation and the magnitude of tensile forces developed in corner columns are relatively more critical. Presence of vertical component of earthquake leads to a drop in minimum compressive force and initiation of tension in columns. The magnitude of this reduction in the most critical case is recorded on average 84% under near-fault ground motions. Besides, the presence of earthquake vertical components increases the shear capacity required in columns, which is at most 31%. In the best case, a direct correlation of 95% between the increase of the maximum compressive force and the ratio of vertical to horizontal „effective peak acceleration (EPA)‟ is observed.

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.

Identification and Representation of Multi-Pulse Near-Fault Strong Ground Motion Using Adaptive Wavelet Transform

In order to identify the horizontal seismic motion owning the largest pulse energy, and represent the dominant pulse-like component embedded in this seismic motion, we used the adaptive wavelet transform algorithm in this paper. Fifteen candidate mother wavelets were evaluated to select the optimum wavelet based on the similarities between the candidate mother wavelet and the target seismic motion, evaluated by the minimum cross variance. This adaptive choosing algorithm for the optimum mother wavelet was invoked before identifying both the horizontal direction owning the largest pulse energy and every dominant pulse, which provides the optimum mother wavelet for the continuous wavelet transform. Each dominant pulse can be represented by its adaptively selected optimum mother wavelet. The results indicate that the identified multi-pulse component fits well with the seismic motion. In most cases, mother wavelets in one multi-pulse seismic motion were different from each other. For the Chi-Chi event (1999-Sep-20 17:47:16 UTC, Mw = 7.6), 62.26% of the qualified pulse-like earthquake motions lay in the horizontal direction ranging from ±15° to ±75°. The Daubechies 6 (db6) mother wavelet was the most frequently used type for both the first and second pulse components.

Semi-active leverage-type isolation system considering minimum structural energy

Semi-active isolation systems based on leverage-type stiffness control strategies have been widely studied. The main concept behind this type of system is to adjust the stiffness in the isolator to match the fundamental period of the isolated system by using a simple leverage mechanism. Although this system achieves high performance under far-field earthquakes, it is unsuitable for near-fault strong ground motion. To overcome this problem, this study considers the potential energy effect in the control law of the semi-active isolation system. The minimal energy weighting (MEW) between the potential energy and kinetic energy was first optimized through a series of numerical simulations. Two MEW algorithms, namely generic and near-fault MEW control, were then developed to efficiently reduce the structural displacement responses. To demonstrate the performance of the proposed method, a two-degree-of-freedom structure was employed as a benchmark. Numerical results indicate that the dynamic response of the structure can be effectively dampened by the proposed MEW control under both far-field and near-fault earthquakes, whereas the structural responses resulting from conventional control methods may be greater than those for the purely passive control method. Moreover, according to experimental verifications, both the generic and near-fault MEW control modes yielded promising results under impulse-like earthquakes. The practicability of the proposed control algorithm was verified.

Destructive near-fault strong ground motion from the 2016 Kumamoto prefecture, Japan, M7.3 earthquake

The sequence of the 2016 Kumamoto, Japan, earthquake, which included an initial M6.5 foreshock on April 14, followed by a larger M7.3 mainshock on April 16, and subsequently occurred high aftershock activity, caused significant damage in Kumamoto and neighboring regions. The near-field strong motion record by strong motion network (K-NET and KiK-net) and the intensity meter network demonstrated clearly the characteristics of the strong ground motion developed by the shallow (H = 12 km), inland earthquake comprising short-time duration ( 1G) ground accelerations. The velocity response spectra of the near-fault motion at Mashiki and Nishihara showed large levels (>300–550 cm/s) in the short-period range (T = 1–2 s), several times larger than that of the near-field record of the destructive 1995 Kobe earthquake (M7.3) and that of the 2004 Mid-Niigata earthquake (M6.8). This period corresponds to the collapse vulnerability of Japanese wooden-frame houses, and is the major cause of severe damage during the Kumamoto earthquake. The response spectra also showed extremely large levels (>240–340 cm/s) in the long-period (T > 3 s) band, which is potentially disastrous for high-rise buildings, large oil storage tanks, etc. to have longer resonant period. Such long-period motion was, for the most parts, developed by the static displacement of the fault movement rather than by the seismic waves radiating from the source fault. Thus, the extreme near-fault long-period motion was hazardous only close to the fault but it attenuated very rapidly away from the fault.

Probabilistic sensitivity analysis of suspension bridges to near-fault ground motion

The sensitivities of a structural response due to variation of its design parameters are prerequisite in the majority of the algorithms used for fundamental problems in engineering as system uncertainties, identification and probabilistic assessments etc. The paper presents the concept of probabilistic sensitivity of suspension bridges with respect to near-fault ground motion. In near field earthquake ground motions, large amplitude spectral accelerations can occur at long periods where many suspension bridges have significant structural response modes. Two different types of suspension bridges, which are Bosporus and Humber bridges, are selected to investigate the near-fault ground motion effects on suspension bridges random response sensitivity analysis. The modulus of elasticity is selected as random design variable. Strong ground motion records of Kocaeli, Northridge and Erzincan earthquakes are selected for the analyses. The stochastic sensitivity displacements and internal forces are determined by using the stochastic sensitivity finite element method and Monte Carlo simulation method. The stochastic sensitivity displacements and responses obtained from the two different suspension bridges subjected to these near-fault strong-ground motions are compared with each other. It is seen from the results that near-fault ground motions have different impacts stochastic sensitivity responses of suspension bridges. The stochastic sensitivity information provides a deeper insight into the structural design and it can be used as a basis for decision-making.

Probabilistic sensitivity analysis of suspension bridges to near-fault ground motion

The sensitivities of a structural response due to variation of its design parameters are prerequisite in the majority of the algorithms used for fundamental problems in engineering as system uncertainties, identification and probabilistic assessments etc. The paper presents the concept of probabilistic sensitivity of suspension bridges with respect to near-fault ground motion. In near field earthquake ground motions, large amplitude spectral accelerations can occur at long periods where many suspension bridges have significant structural response modes. Two different types of suspension bridges, which are Bosporus and Humber bridges, are selected to investigate the near-fault ground motion effects on suspension bridges random response sensitivity analysis. The modulus of elasticity is selected as random design variable. Strong ground motion records of Kocaeli, Northridge and Erzincan earthquakes are selected for the analyses. The stochastic sensitivity displacements and internal forces are determined by using the stochastic sensitivity finite element method and Monte Carlo simulation method. The stochastic sensitivity displacements and responses obtained from the two different suspension bridges subjected to these near-fault strong-ground motions are compared with each other. It is seen from the results that near-fault ground motions have different impacts stochastic sensitivity responses of suspension bridges. The stochastic sensitivity information provides a deeper insight into the structural design and it can be used as a basis for decision-making.

Study on Seismic Safety Performance for Continuous Girder Bridge based on Near-fault Strong Ground Motions

Abstract In order to explore the safety performance of continuous structure bridge near fault zone, a typical three spans continuous girder bridge of highway was selected to study the structural seismic response. The finite element model of whole bridge considered the force characteristics of bearing and pile-soil interaction was constructed. Typical near-fault records were selected from the important earthquake events. Several artificial waves characterized with the soil type in bridge site were simulated and used for dynamic analysis. Comparing with the seismic response of bridge under three given acceleration design spectrum, the seismic performance of continuous bridge was studied by nonlinear dynamic time-history method. Research results indicates that, the seismic design spectrum considering near-fault effect, especially large amplitude pulse effect of near-fault records, will significantly enhance the seismic response of continuous girder bridge. The fact that the near-fault effect is not considered in China existing highway bridge seismic design code will increase the destructive risk of structure.

Erratum to: Effects of air temperature on the cyclic behavior of elastomeric seismic isolators

We found that one of the references in this paper is incorrect. More specifically, George PM (2010) Effect of fault rupture characteristics on near-fault strong ground motions. Bull Seismol Soc Am 100(1):37–58 should be replaced by Mavroeiidis GP and Papageorgiou AS (2010) Effect of fault rupture characteristics on near-fault strong ground motions. Bull Seismol Soc Am 100(1):37–58 In addition, in the sixth paragraph of section 3.2 Effects due to prolonged exposure to low temperatures, “George (2010)” shouldbe replacedby“Mavroeidis andPapageorgiou (2010)”.

Seismic hazard analysis of Tianjin area based on strong ground motion prediction

Taking Tianjin as an example, this paper proposed a methodology and process for evaluating near-fault strong ground motions from future earthquakes to mitigate earthquake damage for the metropolitan area and important engineering structures. The result of strong ground motion was predicted for Tianjin main faults by the hybrid method which mainly consists of 3D finite difference method and stochastic Green’s function. Simulation is performed for 3D structures of Tianjin region and characterized asperity models. The characterized asperity model describing source heterogeneity is introduced following the fault information from the project of Tianjin Active Faults and Seismic Hazard Assessment. We simulated the worst case that two earthquakes separately occur. The results indicate that the fault position, rupture process and the sedimentary deposits of the basin significantly affect amplification of the simulated ground motion. Our results also demonstrate the possibility of practical simulating wave propagation including basin induced surface waves in broad frequency-band, for seismic hazard analysis near the fault from future earthquakes in urbanized areas.

Physics-Based Earthquake Source Characterization and Modeling with Geostatistics

Abstract Physics-based ground-motion simulation requires the development of physically self-consistent source modeling tools to emulate the essential physics of earthquake rupture. Because of the high computational demand of full-dynamic rupture modeling, the kinematic description of earthquake source processes provides the most practical way of covering a wide range of rupture and wave propagation scenarios. We apply 2D spatial data analysis tools, commonly used in geostatistics, to characterizing earthquake rupture process and developing an effective source modeling tool for strong-motion prediction. The earthquake source process is described by key kinematic source parameters, such as static slip, rupture velocity, and slip duration. The heterogeneity of each source parameter is characterized with autocoherence while the linear dependency (coupling) between parameters is characterized with cross coherence. Both zero- and nonzero-offset spatial coherence can be considered in the form of cross coherence. We analyzed both synthetic and real dynamic rupture models to demonstrate the efficiency of these new techniques and found that many important features of earthquake rupture can be captured in this way, which may be difficult to analyze, or even detect by zero-offset coherence only. For instance, the correlation maximum between slip and rupture velocity can be shifted from the zero offset, that is, large slip may generate faster rupture velocity ahead of the current rupture front, which may be important for rupture directivity. We demonstrate that we can generate a number of realizations of earthquake source models to reproduce the target coherence using stochastic modeling techniques (e.g., sequential Gaussian simulation) once coherence structures in earthquake rupture are well understood. This type of coherence analysis may provide the potential for improved understanding of earthquake source characteristics and how they control the characteristics of near-fault strong ground motions.

Effect of Fault Rupture Characteristics on Near-Fault Strong Ground Motions

The effect of fault rupture characteristics on near-fault strong ground motions is investigated using a kinematic modeling approach in an attempt to identify physical processes that lead to specific ground-motion patterns. The shear-stress distribution on the causative fault plane of four well-documented seismic events (i.e., 1979 Imperial Valley, 1985 Michoacan, 1989 Loma Prieta, and 1999 Izmit) is calculated based on fault slip models available in the literature using the methodology proposed by Bouchon (1997) for stress field computations. In order to associate the fault rupture characteristics (i.e., slip, rupture velocity, state of stress) of the investigated earthquakes with near-fault ground motions generated by the events, forward ground-motion simulations are performed using the discrete wavenumber representation method and the concept of the S -wave isochrones is exploited. The results indicate that the seismic energy radiated from the high-isochrone-velocity region of the fault arrives at the receiver within a time interval that coincides with the time window of the long-period ground-motion pulse recorded at the site. Furthermore, the near-fault ground-motion pulses are strongly correlated with large slip on the fault plane locally driven by high stress drop. In addition, the local rupture velocity seems to be inversely correlated to the spatial distribution of the strength excess over the fault plane confirming findings of previous studies. For various events the area of the fault that contributes to the formation of the near-fault pulse encompasses more than one patch of significant moment release (subevent) (e.g., 1979 Imperial Valley, 1989 Loma Prieta). This observation explains why a dislocation model with average properties (i.e., slip, rise time, etc.) reproduces successfully near-fault ground motions for strike-slip faults and for dip-slip faults with intermediate-to-large earthquake magnitudes (Aki, 1979). However, for very large earthquakes, such as megathrust events on subduction zones (e.g., 1985 Michoacan), the fault region that contributes to the pulse formation encompasses individual subevents and, consequently, cracklike slip functions (rather than dislocation models) may be more appropriate for the simulation of the near-fault ground motions.

Near-Fault Strong Ground Motions Recorded during the Morelia Normal-Fault Earthquakes of May 2006 in Mexicali Valley, B. C., Mexico

By the end of May 2006, a series of earthquakes had occurred in the Mexicali Valley, Baja California, Mexico. This activity, which included an M w 5.4 event, developed in the vicinity of the Cerro Prieto geothermal field. The earthquakes occurred on the Morelia fault, one of the east-dipping normal faults in the Mexicali Valley. Cracks and fissures visible on the ground after the stronger earthquake defined two parallel fault segments of 4 and 2 km length, the shorter segment being 1 km to the east of the other one. Down-dip displacements of up to 25–30 cm were measured at some places along this surface break zone. The ten larger events of the series were recorded by strong-motion stations that operate in the epicenter area, so that accurate hypocenter locations were obtained on the basis of P -wave arrival times from the strong-motion recordings. The estimated shallow depths, combined with the earthquake magnitude, explain the strong shaking felt by residents and some damage observed on the Cerro Prieto geothermal plant. The M w 5.4 event produced peak ground accelerations that go from 0.002 g at CUC (on rock) to 0.5 g at GEO (on sediments), at 13 and 1.7 km from the epicenter, respectively. The station GEO recorded closer to the epicenters and on the hanging-wall side of the fault. Static ground displacements and a predominance of the strike-normal over the strike-parallel velocity components were determined from the acceleration records of this station. These and other ground-motion characteristics are also seen on pseudovelocity and absolute acceleration response spectra calculated from data of the larger event. Altogether, the observed ground-motion characteristics provide useful insights into the levels of ground shaking that near-fault structures in the Mexicali Valley should be designed to withstand.