Broadband Ground Motion Research Articles

Broadband Ground Motions from Dynamic Models of Rupture on the Northern San Jacinto Fault, and Comparison with Precariously Balanced Rocks

The Southern California San Jacinto fault is geometrically complex, consisting of several major strands with smaller scale complexity within each strand. The two northernmost strands, the Claremont and the Casa Loma–Clark, are separated by a 25‐km‐long extensional stepover with an average of 4 km separation between the strands. We use a combined modeling method to assess probable rupture and ground‐motion behaviors for this stepover. First, dynamic rupture modeling on geometrically complex fault strands embedded in a state‐of‐the‐art 3D crustal velocity model is used to generate a series of scenario earthquakes. We then use the resulting near‐fault low‐frequency (<1 Hz) ground‐motion time histories to generate broadband synthetic seismograms with a hybrid approach. These synthetics are then compared with a distribution of precariously balanced rocks (PBRs) near the fault to constrain our results and assess shaking hazard for the region surrounding the fault. Our dynamic models produce sources between M w 5.4 and 6.9, with rupture limits imposed by sharp contrasts in fault stress or by geometrical barriers. The main stepover serves as a primary barrier to rupture in our model, producing event sizes that are consistent with the historical behavior of the San Jacinto fault. The largest broadband synthetics are a good match to leading ground‐motion prediction equations and are generally consistent with the distribution of PBRs, none of which experience accelerations that produce toppling probabilities significantly higher than zero. Thus, although the PBRs do not rule out any of our model scenarios, they confirm that our models produce realistic rupture extents and shaking. Online Material: Figures of total slip for additional rupture models, low‐frequency intensity plots, synthetic seismograms, and comparison with ground‐motion prediction equations.

Values for peak ground acceleration and peak ground velocity using in seismic hazard assessment for Song Tranh 2 hydropower region

Values for peak ground acceleration and peak ground velocity using in seismic hazard assessment for Song Tranh 2 hydropower region

PSHA for Broad-Band Strong Ground-Motion Hazards in the Saronikos Gulf, Greece, from Potential Earthquake with Synthetic Ground Motions

We perform a probabilistic seismic hazard analysis (PSHA) for broad-band strong ground motion within the Saronikos Gulf region, Greece, from potential earthquakes along the 30 km long Aigina fault in the northern part of the Gulf. We perform the PSHA utilizing empirical Green’s functions (EGFs) merged with synthetic Green’s functions (SGFs) along with models of finite rupture in place of standard “attenuation relations.” Our approach considers all significant magnitudes for PSHA and full broadband ground motion simulations. Calculations are source and site specific, and could reduce uncertainties in estimating standard engineering parameters. We use a range of rupture scenarios for all significant magnitude earthquakes along the fault. The hazard calculation is for frequencies 0.0– 15.0 Hz. Recordings of small earthquakes from an onshore/offshore local seismic array were used as EGFs for frequencies of 1.5–15.0 Hz, the finite difference code E3D was utilized to synthesize SGFs for frequencies 0.0–1.5 Hz, and an algorithm for merging the EGFs with SGFs was developed. The full-waveform calculations are important for non-linear dynamic analysis of structures in the coastal zone and potential hazard to long period structures. Results of proposed PSHA identify 2%, 10%, and 50% hazard at the selected sites of Saronikos Gulf.Finally, we compare our PSHA results to those obtained by standard practice which involves prediction equations (GMPEs) recently developed in the Next Generation Attenuation (NGA) project and empirical predictive attenuation relations proposed for Greece. We believe that differences with the NGA results are due to site- and source-specific information utilized in this study, and incorporation of this information may significantly reduce the uncertainty in seismic hazard calculations.

UCSB Method for Simulation of Broadband Ground Motion from Kinematic Earthquake Sources

The representation theorem (equation 1.1) (Maruyama, 1963; Burridge and Knopoff, 1964; Haskell, 1964) relates slip on the fault to ground displacement at an arbitrary point in the field and can be deceptively simple as follows: ![Graphic][1] (1.1)in which ![Graphic][2] is the n th component of the ground displacement recorded at position ![Graphic][3] and time t ; ![Graphic][4] is the i th component of slip (a discontinuity in displacement field) on the fault plane Σ at position ξ and time τ ; ν j is the j th component of the normal to fault plane, c ijpq is the fourth‐order tensor of elastic coefficients; is the n th component of the Green’s function for a point source applied in the p direction. The integral over d Σ is the summation over the fault of the convolution (the integral of dτ ) between the slip on the fault and the spatial derivative of the Green’s function G np , q . So all one needs is the geometry of the fault plane (Σ and ν j ), an accurate description of the medium (densities, elastic velocities, and attenuation in 3D space) to compute G np , and the slip‐time function ![Graphic][5] everywhere on the fault. Suppose one has a particular location ![Graphic][6] where the ground motion is to be computed from an earthquake on a specified fault. The first step would be to use reciprocity of the Green’s function and apply the point forces at the location of the observer to compute the tractions ![Graphic][7] on the fault (Archuleta and Day, 1980; Spudich and Archuleta, 1987). Because one cannot compute tractions everywhere on the fault, one has to decide a priori on the locations for which the tractions are to be computed. Moreover computing the tractions assumes that one knows the velocity, density, and attenuation structure throughout … [1]: /embed/inline-graphic-1.gif [2]: /embed/inline-graphic-2.gif [3]: /embed/inline-graphic-3.gif [4]: /embed/inline-graphic-4.gif [5]: /embed/inline-graphic-5.gif [6]: /embed/inline-graphic-6.gif [7]: /embed/inline-graphic-7.gif

Seismic response of sliding equipment and contents in base‐isolated buildings subjected to broadband ground motions

SummaryBase isolation has been established as the seismic design approach of choice when it comes to protecting nonstructural contents. However, while this protection technology has been widely shown to reduce seismic demands on attached oscillatory equipment and contents (EC), its effectiveness in controlling the response of freestanding EC that are prone to sliding has not been investigated. This study examines the seismic behavior of sliding EC inside base‐isolated buildings subjected to broadband ground motions. The effect of isolation system properties on the response of sliding EC with various friction coefficients is examined. Two widely used isolation models are considered: viscously damped linear elastic and bilinear. The study finds isolation to be generally effective in reducing seismic demands on sliding EC, but it also exposes certain situations where isolation in fact increases demands on EC, most notably for low friction coefficients and high earthquake intensities. Damping at the isolation level is effective in controlling the EC sliding displacements, although damping over about 20% is found to be superfluous. The study identifies a physically motivated dimensionless intensity measure and engineering demand parameter for sliding equipment in base‐isolated buildings subjected to broadband ground motions. Finally, the paper presents easy‐to‐use design fragility curves and an example that illustrates how to use them. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Bias assessment in Incremental Dynamic Analysis due to record scaling

Incremental Dynamic Analysis (IDA) involves a series of nonlinear response history analyses with a suite of incrementally scaled ground motion records. Although IDA is perhaps the most comprehensive seismic performance assessment method, it receives criticism because several ground motion records are scaled up until the structure collapses. The scaling practice often results to unrealistic multipliers, thus modifying the amplitude of the ground motion and introducing bias on the structural performance estimation. Record scaling is a common practice in earthquake engineering due to the lack of natural records corresponding to large magnitudes and/or small distances from the fault rupture location. In this work we use a large number of ground motion records to compare the predictions of IDA with that of unscaled ground motions and we propose a new methodology in order to quantify the bias introduced in IDA. Apart from natural records, we have conducted broadband ground motion simulations for rupture scenarios of weak, medium and large magnitude events in order to expand our record database. The investigation is performed on a series of inelastic single-degree-of-freedom systems and on two multistory steel moment frame buildings. The results pinpoint both qualitatively and quantitatively, for the full range of limit-states, the bias that IDA introduces on the structural performance estimation.

Demand Diagrams Based on Inelastic Spectra: A Proposal for the Implementation of the Capacity Spectrum Method in the Romanian Seismic Design Code

During recent years, an increasing number of studies advocate the application of the capacity spectrum method based demand diagrams computed directly from inelastic response spectra, as an alternative to the basic formulation of the method, which uses elastic spectra computed for single degree-of-freedom oscillators with modified characteristics to account for inelastic behavior. When demand diagrams are based on the code-specified elastic spectrum, inelastic spectra are typically determined by dividing the elastic spectrum by strength reduction factors. The paper presents the application of the method, based on strength reduction factors computed with a unified analytical expression, deduced by the author in previous studies. The expression and is valid both for broadband and narrow band ground motions. Taking as a starting point the newly-enforced elastic design spectra in the 2013 edition of the Romanian seismic design code, the method is exemplified for the capital city, Bucharest. It is shown that, for the analyzed case, the use of the proposed strength reduction factors leads to results that are very close to those obtained by the “classical” nonlinear static procedure used in the code. This suggests a good potential for the implementation of the capacity spectrum method in the Romanian code, based on these factors.

Variability in Wood-Frame Building Damage using Broad-Band Synthetic Ground Motions: A Comparative Numerical Study with Recorded Motions

Earthquake damage to light-frame wood buildings is a major concern for North America because of the volume of this construction type. In order to estimate wood building damage using synthetic ground motions, we need to verify the ability of synthetically generated ground motions to simulate realistic damage for this structure type. Through a calibrated damage potential indicator, four different synthetic ground motion models are compared with the historically recorded ground motions at corresponding sites. We conclude that damage for sites farther from the fault (>20 km) is under-predicted on average and damage at closer sites is sometimes over-predicted.

Calibration of a Semi-Stochastic Procedure for Simulating High-Frequency Ground Motions

Broadband ground motion simulation procedures typically utilize physics-based modeling at low frequencies, coupled with semi-stochastic procedures at high frequencies. The high-frequency procedure considered here combines deterministic Fourier amplitude spectra (dependent on source, path, and site models) with random phase. Previous work showed that high-frequency intensity measures from this simulation methodology attenuate faster with distance and have lower intra-event dispersion than in empirical equations. We address these issues by increasing crustal damping (Q) to reduce distance attenuation bias and by introducing random site-to-site variations to Fourier amplitudes using a lognormal standard deviation ranging from 0.45 for Mw &lt; 7 to zero for Mw 8. Ground motions simulated with the updated parameterization exhibit significantly reduced distance attenuation bias and revised dispersion terms are more compatible with those from empirical models but remain lower at large distances (e.g., &gt; 100 km).

Fault Process and Broadband Ground-Motion Simulations of the 23 October 2011 Van (Eastern Turkey) Earthquake

Abstract On 23 October 2011 an M w 7.1 earthquake occurred in eastern Turkey, close to the towns of Van and Ercis, causing more than 600 casualties and widespread structural damage. The earthquake ruptured a 60–70 km long northeast–southwest fault with a thrust mechanism, in agreement with regional tectonic stress regime. We studied the fault process of the event and the recorded ground motions using different sets of data. Regional records (0.005–0.010 Hz) are used to constrain the centroid moment tensor solution. Near‐regional data, 100–200 km from the fault, are used for relocation of the hypocenter and, in the frequency range 0.05–0.15 Hz, for inversion of the rupture propagation by two methods: multiple point‐source model (ISOLA) and multiple finite‐extent (MuFEx) source model. MuFEx also provides an estimate of the model uncertainty, which is quite large due to unfavorable station distribution. We arrive at several plausible scenarios (equally well fitting the observed data including Global Positioning System coseismic displacements) with different styles of the rupture propagation. A few alternative source models are used for broadband (0.1–10 Hz) ground‐motion simulations by means of the hybrid integral‐composite source model. Only models comprising source complexities, such as a delayed rupture of shallow asperities, enable explanation of the acceleration record at the only available near‐fault station, which exhibits a long duration and two prominent wave groups. These complex rupture models are used to simulate the ground motion in the near‐fault area, specifically, at Van and Ercis, where records of the mainshock were missing, providing reasonable agreement with the observed spatial distribution of damage.

Modeling of the Subsurface Structure from the Seismic Bedrock to the Ground Surface for a Broadband Strong Motion Evaluation

Sophisticated predictions of strong ground motion are vital when constructing structure models that enable us to evaluate broadband ground motion features. Such models should integrate subsurface structure models for strata shallower than engineering bedrock and deep structuremodels for strata even deeper. Both such models used to be separately modeled separately so that observation data could be reproduced. In this study, we have created a subsurface structure model applicable from seismic bedrock to ground surface for individual Japanese individual prefectures, e.g., Chiba and Ibaragi, in attempts to sophisticate subsurface structure models. This paper describes how we created these models and reviews our results.

Influence of Hysteretic Behavior on Seismic Strength Demands: An Analysis for Romanian Vrancea Earthquakes

The paper presents the results of a study performed on a large ground motion database, containing records obtained during the three strongest earthquakes that occurred during the past four decades in the Vrancea seismogenic zone. In order to express strength demands imposed by these earthquakes, constant-ductility nonlinear acceleration spectra were computed for two sets of seismic records, selected as representative for narrow frequency band and broad frequency band ground motions, respectively. The spectra, determined for various types of bilinear hysteretic models, were normalized with respect to peak ground acceleration and mean values, as well as coefficients of variation, were computed for each analysis case. The sensitivity of spectral values to the variation of strength hardening and stiffness degradation parameters was determined, with reference to the elastic-perfectly plastic model. Conclusions were drawn, separately for the two distinct types of ground motion frequency content, on the significance of the considered hysteretic model parameters for the assessment of seismic strength demands.

Strength Reduction Factors: A Unified Analytic Expression for Narrowband and Broadband Ground Motion Records

Strength reduction factors are an important component of the force modification factors used in the calculation of seismic code forces, as they account for the effect of the nonlinear hysteretic behavior of the structure. They are expressed as the ratio between the elastic strength demand and the inelastic strength demand induced in a structure by the earthquake. The evaluation of strength reduction factors has applications in the substantiation of seismic force modification factors in building design codes and in the direct application of the capacity spectrum method. The paper presents a study performed on two sets of accelerograms having different spectral content types, i.e. narrow frequency band records and broad frequency band records. Based on constantductility spectra of strength reduction factors, computed with 50% and 10% probability of exceedance, a unified analytic formula is developed, to describe the variation with ductility and vibration period of these factors. By modifying the values of the coefficients of the variables, the formula can be adapted for each type of spectral content. The formula is further refined, by determining a new set of coefficients, to also account for the influence of the predominant period of the ground motion in the case of narrow frequency band records.

Broadband Ground-Motion Simulation of an Intraslab Earthquake and Nonlinear Site Response: 2010 Ferndale, California, Earthquake Case Study

Intraslab earthquakes are generated by fault ruptures, which occur at shallow (20–60 km) or deep (>60 km) parts of a subducting tectonic plate slab. In both cases the rupture occurs in the vicinity of a zone with large velocity contrast and increased regional stress caused by the subducting plates. These conditions have significant effects on fault geometry, rupture dynamics, and seismic energy, which in turn affect the amplitude and duration of ground motion. Consequently, intraslab earthquakes can generate larger ground motion than shallow crustal earthquakes of same magnitude. Therefore their study is very important for strong ground motion prediction and seismic‐hazard assessment. In an effort to develop a methodology for simulating strong ground motion from intraslab earthquakes we tested the broadband ground‐motion simulation technique of Graves and Pitarka (2010) in modeling ground motion recorded from the M 6.5 2010 Ferndale, California, intraslab earthquake. The Graves and Pitarka (2010) method was originally developed for simulating crustal earthquakes. To our knowledge this is the first attempt to apply a broadband ground‐motion‐simulation method in modeling ground motion from intraslab earthquakes in the United States. A similar approach (Matsuzaki et al. , 2010) was applied to studying the rupture process of the 2001 Geiyo, Japan, intraslab earthquake using the recipe developed by Irikura and Miyake (2006). In this study we simulate and analyze ground‐motion‐acceleration time history recorded during the earthquake in a zone between Ferndale and Eureka, and Humboldt Bay. The earthquake was very well recorded in a geotechnical array located in the Humboldt Bay soft sediments. The ground‐motion acceleration recorded by the array’s instruments at several depths provided a good opportunity for testing numerical techniques and empirical models of the nonlinear seismic response of soils for input motion with moderate amplitude. A large part of our investigation is focused on modeling the observed nonlinear response …

Cost‐effective monitoring of ground motion related to earthquakes, landslides, or volcanic activity by joint use of a single‐frequency GPS and a MEMS accelerometer

AbstractReal‐time detection and precise estimation of strong ground motion are crucial for rapid assessment and early warning of geohazards such as earthquakes, landslides, and volcanic activity. This challenging task can be accomplished by combining GPS and accelerometer measurements because of their complementary capabilities to resolve broadband ground motion signals. However, for implementing an operational monitoring network of such joint measurement systems, cost‐effective techniques need to be developed and rigorously tested. We propose a new approach for joint processing of single‐frequency GPS and MEMS (microelectromechanical systems) accelerometer data in real time. To demonstrate the performance of our method, we describe results from outdoor experiments under controlled conditions. For validation, we analyzed dual‐frequency GPS data and images recorded by a video camera. The results of the different sensors agree very well, suggesting that real‐time broadband information of ground motion can be provided by using single‐frequency GPS and MEMS accelerometers.

Prediction of Broadband Ground-Motion Time Histories: The Case of Tehran, Iran

The northern Tehran fault (NTF) is potentially capable of causing large earth-quakes (Mmax~ 7.2) in a very densely populated area of northern Tehran, Iran. Due to the lack of recorded strong motion data for earthquakes on the fault, a hybrid simulation method is used to calculate broadband (0.1–20 Hz) ground-motion time histories at bedrock level for deterministic earthquake scenarios on the NTF. Low-frequency components of motion (0.1–1.0 Hz) are calculated using a deterministic approach and the discrete wave number-finite element method in a regional one-dimensional (1-D) velocity model. High frequencies (1.0–20.0 Hz) are calculated by the stochastic finite fault method based on dynamic corner frequency. The results were validated by comparing the simulated peak values and response spectra with the empirical ground motion models available for the area and the Modified Mercalli intensity (MMI) observations from historical earthquakes of the region.

Validation of Ground-Motion Simulations for Historical Events Using SDoF Systems

The study presented in this paper is among the first in a series of studies toward the engineering validation of the hybrid broadband ground-motion simulation methodology by Graves and Pitarka (2010). This paper provides a statis- tical comparison between seismic demands of single degree of freedom (SDoF) systems subjected to past events using simulations and actual recordings. A number of SDoF systems are selected considering the following: (1) 16 oscillation periods between 0.1 and 6 s; (2) elastic case and four nonlinearity levels, from mildly inelastic to severely inelastic systems; and (3) two hysteretic behaviors, in particular, nondegrading-nonevolutionary and degrading-evolutionary. Demand spectra are de- rived in terms of peak and cyclic response, as well as their statistics for four historical earthquakes: 1979 Mw 6.5 Imperial Valley, 1989 Mw 6.8 Loma Prieta, 1992 Mw 7.2 Landers, and 1994 Mw 6.7 Northridge. The results of this study show that both elastic and inelastic demands from simu- lated and recorded motions are generally similar. However, for some structural sys- tems, the inelastic response to simulated accelerograms may produce median demands that appear different from those obtained using corresponding recorded motions. The magnitude of such differences depends on the SDoF period, the nonlinearity level, and, to a lesser extent, the hysteretic model used. In the case of peak response, these dis- crepancies are likely due to differences in the spectral shape, while the differences in terms of cyclic response can be explained by some integral parameters of ground motion (i.e., duration-related). Moreover, the intraevent standard deviation values of structural demands calculated from the simulations are generally lower than those given by recorded ground motions, especially at short periods. The assessment of the results using formal statistical hypothesis tests indicates that, in most cases, the dif- ferences found are not significant, increasing the trust in the use of simulated motions for engineering applications.

3D Simulations of M 7 Earthquakes on the Wasatch Fault, Utah, Part II: Broadband (0-10 Hz) Ground Motions and Nonlinear Soil Behavior

Abstract We predict broadband (BB, 0–10 Hz) ground motions for M 7 earthquakes on the Salt Lake City segment of the Wasatch fault (WFSLC), Utah, which include the effects of nonlinear site response. The predictions are based on low‐frequency (LF, 0–1 Hz) finite‐difference (FD) simulations for six different rupture models generated during a previous study (Roten et al. , 2011), which we combine with high‐frequency (HF, 1–10 Hz) shear‐to‐shear (S‐to‐S) back‐scattering operators to generate BB synthetics. Average horizontal spectral accelerations at 5 and 10 Hz (0.2‐s SAs and 0.1‐s SAs, respectively) calculated from the linear BB synthetics exceed estimates from four recent ground‐motion prediction equations (GMPEs) at near‐fault ( g on the hanging‐wall side of the fault. Geometric mean 0.2‐s SAs exceed 1 g on the hanging‐wall and on the footwall sediments in the central Salt Lake basin, and peak horizontal ground accelerations range from 0.45 to >0.60 g in the same general locations. Online Material: Table of coefficients and amplitude‐dependent correction functions for nonlinear soil effects, and figures showing maps of SAs at various frequencies, PGA and PGV, with and without correction for nonlinear soil effects, results of 1D nonlinear simulations, and comparison to ground motion prediction equations.

Sensitivity of ground-motion scenarios to earthquake source parameters in the Tehran metropolitan area, Iran

The northern Tehran fault (NTF) is a principal active fault of the Alborz mountain belt in the northern Iran. The fault is located north of the highly populated Metropolitan Area of Tehran. Historical records and paleoseismological studies have shown that the NTF poses a high seismic risk for the Tehran region and the surrounding cities (e.g. Karaj). A series of ground-motion simulations are carried out using a hybrid kinematic-stochastic model to calculate broadband (0.1–20Hz) ground-motion time histories for deterministic earthquake scenarios (M7.2) on the NTF. We will describe the source characteristics of the target event to develop a list of scenario earthquakes that are probably similar to a large earthquake on the NTF. The effect of varying different rupture parameters such as rupture velocity and rise time on the resulting broadband strong motions has been investigated to evaluate the range of uncertainty in seismic scenarios. The most significant parameters in terms of ground-shaking level are the rise time and the value of the rupture velocity. For the worst-case scenario, the maximum expected horizontal acceleration, and velocity at rock sites in Tehran range between 128 and 1315cm/s/s and 11–191cm/s, respectively. For the lowest scenario, the corresponding values range between 102 and 776cm/s/s and 12 to 81cm/s. Nonlinear soil effects may change these results but are not accounted for in this study. The largest variability of ground motion is observed in neighborhood of asperity and also in the direction of rupture propagation. The calculated standard deviation of all ground-motion scenarios is less than 30% of the mean. The capability of the simulation method to synthesize expected ground motions and the appropriateness of the key parameters used in the simulations are confirmed by comparing the synthetic peak ground motions (PGA, PGV and response spectra) with empirical ground-motion prediction equations.

Low-frequency and broad-band source models for the 2009 L’Aquila, Italy, earthquake

SUMMARY The 2009 L’Aquila, Italy, earthquake (Mw 6.3) produced an unprecedented number of seismological records for a normal faulting event, and hence represents an important case study of damaging moderate magnitude earthquakes occurring in densely inhabited areas. We have investigated the source process of the 2009 L’Aquila earthquake in both the low- and broad-band frequency ranges by analysing the teleseismic and strong motion data. A low-frequency (<0.5 Hz) source model has been determined by waveform inversion of teleseismic and near-field strong motion data, yielding slip distributions with a major asperity located about 8 km southeast of the hypocentre. The broad-band (0.2–10 Hz) source characteristics were estimated using the empirical Green's function method providing the strong motion generation area of about 42 km2 located southeast of the hypocentre below the village of Onna. This coincides with the location of the asperity from the inversion analysis, indicating that the low-frequency and broad-band ground motions produced during the earthquake were generated at similar locations on the fault plane. The position of the strong motion generation area also correlates well with the distribution of observed macroseismic (MCS) intensities reported by INGV. The maximum macroseismic intensities of IX–X were reported southeast of the epicentre, with an intensity of X measured in Onna. The source properties of the 2009 L’Aquila mainshock reveal the estimated size of the strong motion generation area to be in agreement with predictions made using empirical source scaling relation for inland crustal earthquakes, implying a stress drop of approximately 10 MPa. This further indicates that the 2009 L’Aquila earthquake involved a stress drop similar to that of previously recorded earthquakes in the Central and Southern Apennines.