Evaluation of Earthquake Response Spectra Directionality Using Stochastic Simulations

ABSTRACT For earthquake-resistant design purposes, ground-motion intensity is usually characterized using response spectra. The amplitude of response spectral ordinates of horizontal components varies significantly with changes in orientation. This change in intensity with orientation is commonly known as ground-motion directionality. Although this directionality has been attributed to several factors, such as topographic irregularities, near-fault effects, and local geologic heterogeneities, the mechanism behind this phenomenon is still not well understood. This work studies the directionality characteristics of earthquake ground-motion intensity using synthetic ground motions and compares their directionality to that of recorded ground motions. The two principal components of horizontal acceleration are sampled independently using a stochastic model based on finite-duration time-modulated filtered Gaussian white-noise processes. By using the same stochastic process to sample both horizontal components of motion, the variance of horizontal ground acceleration has negligible orientation dependence. However, these simulations’ response spectral ordinates present directionality levels comparable to those found in real ground motions. It is shown that the directionality of the simulated ground motions changes for each realization of the stochastic process and is a consequence of the duration being finite. Simulated ground motions also present similar directionality trends to recorded earthquake ground motions, such as the increase of average directionality with increasing period of vibration and decrease with increasing significant duration. These results suggest that most of the orientation dependence of horizontal response spectra is primarily explained by the finite significant duration of earthquake ground motion causing inherent randomness in response spectra, rather than by some physical mechanism causing polarization of shaking.

Effect of Aftershock Characteristics on the Fragility Curve of Post-Mainshock RC Frames

Buildings constructed in seismic zones are not only damaged by mainshocks but may also be damaged by the impact of aftershocks and cause them to collapse. Therefore, studying the behavior of the damaged structures due to the mainshock and aftershock helps in post-mainshock decision making and also in the selection of suitable aftershock records for seismic assessing of the structure under earthquake sequences. This paper presents the effects of aftershock ground motion on the collapse capacity of post-mainshock buildings. The mean period (Tm), predominant velocity period (Tg), frequency bandwidth (Ω), the 5%-95% significant duration (Ds) and seismic records of different sites were selected to evaluate the effect of its characteristics on the collapse capacity of buildings. The intensity of the ground motions was determined by the first-mode spectral acceleration with 5% damping. Collapse capacities of two non-ductile reinforced concrete (RC) frames with 3 and 6 stories were evaluated using a set of 62 aftershock records with a wide range of characteristics. Box plot collapse diagrams and fragility curves have been developed by applying the incremental dynamic analysis (IDA). The results show that in the frequency content with a longer period, the probability of its collapse is higher. In addition, the high significant duration of aftershocks increases the collapse probability of structures. Also, the evaluation of the site characteristics shows differences in collapse capacities of the same frames in varying sites. Therefore, the effect of aftershock characteristics on the capacity of the structures is significant and it is necessary to carefully determine the seismic sequences’ recordings for the evaluation of the seismic behavior of the structures.

Ground motion prediction equations for significant duration using the KiK-net database

Significant duration of strong shaking quantifies the length of time during which strong earthquake-induced shaking occurs at a given site. Significant duration has multiple applications in Geotechnical and Structural Engineering. However, while multiple ground motion prediction (GMPE) equations for duration exist for shallow crustal tectonic environments, at the time of this publication, there are few published models for predicting significant duration of subduction earthquakes. To address this need and to identify the difference between significant duration of motions resulting from earthquakes in different tectonic regimes, we develop predictive equations for significant duration applicable to interface and intraslab subduction earthquakes and shallow crustal earthquakes in active tectonic regimes using the KiK-net ground motion database. The GMPEs are applicable to earthquakes with M4 to 9. In addition, the influence of earthquake magnitude on duration due to path effects is captured in the proposed relationships. Based on the relationships proposed in this study, we note that the duration of ground motions from subduction earthquakes is longer than those of shallow crustal earthquakes that have similar magnitudes and distances. The predictions of duration for shallow crustal earthquakes in active tectonic regimes developed in this study are consistent with those from previous studies.

Ground-Motion Duration Prediction Model from Recorded Mexican Interplate and Intermediate-Depth Intraslab Earthquakes

ABSTRACT Predictive models for ground-motion duration of Mexican subduction interplate and intermediate-depth intraslab earthquakes are presented. The considered sites are rock sites. For the ground-motion duration models, the significant durations for ranges between 5%–75%, 5%–95%, and 2.5%–97.5% of Arias intensity are considered for the analyses. The significant duration predictive models are expressed in terms of magnitude, distance, and focal depth; this last variable is considered only for intraslab earthquakes. A total of 418 and 366 accelerograms obtained from 40 Mexican interplate and 23 intraslab earthquakes, respectively, are used. The applicability of the duration equation for subduction interplate events is restricted to moment magnitudes 5<Mw<8 and distances to the fault surface 17<R<400 km; for intraslab events, it is restricted to 5.2<Mw<8.2, 22<R<400 km, and focal depths 35<HD<75 km. The models are compared against existent models for Mexico and other regions. The analyses and comparisons indicate that using ground-motion duration models accounting for the two types of earthquakes is required and that such models should be developed for specific regions.

Empirical Correlations between Generalized Ground-Motion Intensity Measures for Earthquakes in China

ABSTRACT This study used earthquake records from China to investigate comprehensively the correlation coefficients between various intensity measures (IMs), including peak ground acceleration, peak ground velocity, spectral acceleration, spectrum intensity, acceleration spectrum intensity, Arias intensity, cumulative absolute velocity, and significant duration. After collection of metadata information, 681 three-component ground-motion recordings with magnitudes of Mw 4.9–6.9 were carefully processed and extracted from the China National Strong-Motion Observation Network System dataset (2007–2015). The applicability of both the Next Generation Attenuation (NGA)-West2 ground-motion model (GMM) and of other GMMs was verified for different IMs, regarding the China dataset. Then, empirical correlation coefficients between different IMs were computed, considering the uncertainty due to the different sample sizes of the observational data using the bootstrap sampling method and Fisher z transformation. Finally, the median values of the correlation coefficients were fitted as a continuous function of the vibration period in the range of 0.01–10.0 s and compared with the results of similar studies developed for shallow crustal regions worldwide. The developed region-specific correlation coefficient prediction model yielded tendencies approximately like those reported in other studies. However, obvious differences were found in long-period ranges of amplitude-based IMs, cumulative effect IMs, and significant duration. These results suggest the necessity of using region-specific correlation coefficients for generalized IMs in China. The presented results and parametric models could be easily implemented in a generalized IM ground-motion selection method or a vector-based probability seismic hazard analysis procedure for China.

Ground-Motion Models for the Prediction of Significant Duration Using Strong-Motion Data from Iran

ABSTRACT In this study, new prediction equations for significant duration (DS5–75 and DS5–95) are developed using an Iranian strong ground-motion database. The database includes 2228 records of 749 earthquakes with small to large magnitudes up to the year 2018. The functional form of the model is an additive natural logarithm of four predictor variables, namely moment magnitude (Mw), rupture distance (Rrup), time-averaged shear-wave velocity in the top 30 m (VS30), and the style of faulting effect (Fm), which is considered as an indicator directly in the functional form for the first time. The proposed models can be used to estimate significant durations of earthquakes with moment magnitudes (Mw) from 4.5 to 7.6 and rupture distances of up to 200 km. The models are compared with four existing significant-duration prediction models. The results indicate proper agreement between the proposed models and the models that use the Pacific Earthquake Engineering Research Center-Next Generation Attenuation-West2 Project (PEER-NGA West2) database (say PEER models). Based on the results, our proposed models indicate an increasing trend of significant duration with an increase in the rupture distance. However, unlike the PEER models, the rate of increase in significant duration is decreasing in our model.

Duration of the phase of preservation and destruction in cases of deposits of iced categories of SHP (spontaneous) in the territory of Ukraine in the month of the cold period of the year during 1991–2016

The article deals with the question of the duration of the preservation and destruction phase which were calculated for ice-free periods of the category of SHP and were observed on the territory of Ukraine in the month of the cold period of the year during certain periods 1991–2000, 2001-2010 and 2011-2016. It was established that the duration of the preservation phase and the destruction of ice-oily deposits in the category of SHP is very volatile and ranges from near-instant destruction after reaching a maximum diameter of several hours or several dozen hours. However, there are cases where the duration of this phase can be 4 days in a row and more than several hundred hours. The study found that for the most part during the investigated period, the glacial deposits of the SHP category were dominated by non-prolonged conservation and degradation phases, regardless of the region where the sediment was formed, and regardless of the overall duration of the sediment itself, which could be significant. In 2001–2010 and 2011–2016, unlike in the period of 1991-2000, in January and December, the number of cases of ice-ousted categories of SHP increased. Moreover, in January, especially in 2011–2016, the number of cases with a significant duration of the phase of preservation and destruction of ice deposits of the category of SHP was increased. From the above we can draw a number of conclusions, namely: – During 1991–2000, the phases of preservation and destruction of ice-clay deposits in the category of HPAs were mostly non-prolonged and ranging from several hours to several dozen hours. The most prolonged phases of preservation and destruction of deposits of iced ice of category SHHA were in cases of sediments in Lower Zirgozakh in January 1996, in March 1998 in Kropivnitsky and most often in November 1999 in Gadyach, Dolynska, Komissarivka, Mariupol, Prisheby, and also in 2000 It is in Novodnistrovsk, Separate, Lyubashevtsi, Serbs, Voznesensk, December 1997 in Loshkarivka, Kryvy Rih, Nikopol, Lyubashevtsi, Prisheb and especially in Donetsk. – In 2001–2010, the amount of ice-cream deposits in the category of SHP increased slightly. In addition, the duration of the preservation and destruction phase compared to the previous period changed slightly, taking into account the individual months. So, in January, along with the relatively long phases of preservation and destruction of ice-clay deposits of the category of SHP (up to several dozen hours), in 2010 deposits with very long phases of conservation and destruction in Debaltsevo and especially in Mysovoye were observed. In December of this period, the long phases of preservation and destruction of deposits of iced ice of category SHP were observed in 2004 in Dar’yivka, and in 2008 in Vinnitsa and Ovruch. In the remaining months, the duration of the conservation and destruction phase was overwhelmingly within a few hours, at least to several dozen golds (11–25 hours) – Unlike in the years 1991-2000 and 2001-2010, in January the number of cases of ice deposits of the category of SHP increased in the five-year period of 2011–2016. They met practically in most regions. Significantly increased cases with them, where the duration of the preservation and destruction phase was significant and exceeded the duration of 4 consecutive days. Such cases were observed in January 2013 in Rava-Ruska, Kamianets Buzka and Poltava, in January 2014 – in Rava-Ruska, Ternopil, Amvrosiyivka, Rosdilna, Mykolayiv, Ochakov, and Simferopol. In December 2012, a similar accident happened in Evpatoria.

Quantification of the Influence of Deep Basin Effects on Structural Collapse Using SCEC CyberShake Earthquake Ground Motion Simulations

This paper examines the effects of earthquake ground motions in deep sedimentary basins on structural collapse risk using physics-based earthquake simulations of the Los Angeles basin developed through the Southern California Earthquake Center's CyberShake project. Distinctive waveform characteristics of deep basin seismograms are used to classify the ground motions into several archetype groups, and the damaging influence of the basin effects are evaluated by comparing nonlinear structural responses under spectrum and significant duration equivalent basin and nonbasin ground motions. The deep basin ground motions are observed to have longer period-dependent durations and larger sustained spectral intensities than nonbasin motions for vibration periods longer than about 1.5 s, which can increase structural collapse risk by up to 20% in ground motions with otherwise comparable peak spectral accelerations and significant durations. Two new metrics are proposed to quantify period-dependent duration effects that are not otherwise captured by conventional ground motion intensity measures. The proposed sustained amplitude response spectra and significant duration spectra show promise for characterizing the damaging effects of long duration features of basin ground motions on buildings and other structures.