Strong Motion Characteristics Research Articles

Sensitivity analysis of input ground motion on surface motion parameters in high seismic regions: a case of Bhutan Himalaya

Abstract. Historical earthquakes demonstrate that strong motion characteristics and local soil condition, when coupled, significantly influence seismic site response. Interestingly, most of the Himalayan earthquakes depicted anomalous behavior per the site conditions historically. Being one of the most active seismic regions on earth, the eastern fringe of the Himalaya has observed many devastating earthquakes together with non-uniform damage scenarios. To quantify such anomalies, we evaluate surface motion parameters for a soft soil deposit located in the city of Phuentsholing in western Bhutan. Using one-dimensional site response analysis, the sensitivity of ground motion variation is estimated. This study accounts for the earthquakes of moment magnitudes 6.6 to 7.5 with a wide variation in peak ground acceleration (PGA). To dissect the characteristics of six inputted ground motions on eight local ground conditions, a sensitivity analysis is performed statistically. The statistical correlation of the response datasets and the linear regression model of the bedrock outcrop and the surface motion spectral acceleration along the stratified depth are examined to quantify the variation in surface motion parameters. The results highlight that the strong motions with PGA greater than 0.34 g demonstrate greater sensitivity, leading to some anomalies in response parameters, especially amplification. Similar results were obtained for the low PGA range (<0.1 g).

Spectral matching RotD100 target spectra: Effect on records characteristics and seismic response

This article investigates three different approaches to generate seismic input compatible with RotD100 design spectra: (1) separately matching each horizontal component to the target spectrum, (2) separately matching and then scaling-down the records to improve the match and (3) directly pursuing the match of RotD100 by simultaneously modifying both horizontal components. We examine the strong motion characteristics of the resulting records individually and their variability as suites of input records. The records generated, along with a set of amplitude-scaled records, are used as input for bi-directional non-linear response history analyses of idealized single column reinforced concrete bridge piers with different geometric and reinforcement characteristics. It is shown that the records generated pursuing a direct match of the target spectrum attain the closest match, retain better the strong motion characteristics of the seed records and their horizontal components exhibit a spectral variability comparable to suites of amplitude-scaled records. Regarding the effect on seismic response, the suites constructed separately matching each component consistently imposed larger peak inelastic and total energy demands than all other suites. Directly pursuing the match of RotD100 generated responses close but consistently below the expected from amplitude-scaled suites. The best results were obtained using the direct match methodology but using as target 110% the RotD100 spectrum as required in ASCE 7-16.

Source and strong-motion characteristics of two M\u2009>\u20096 buried earthquakes in southwest Taiwan

We used near-field strong-motion data to investigate the complex combination of source effect and site response for two recent disastrous earthquakes in southwest Taiwan. We estimated strong-motion generation areas (SMGAs) of 2.8 km × 2.8 km and 6.0 km × 4.2 km in a frequency band of 0.4–10 Hz for the 2010 Jiashian and 2016 Meinong earthquakes, respectively. The high-stress drops of 26.2 and 17.0 MPa for these two buried events were potentially related to the small dimension and deep rupture. Our results revealed that both earthquakes exhibited westward rupture directivity, whereas the 2016 Meinong event exhibited a stronger directivity effect because of the consistency between the propagation and slip directions. The localized high peak ground velocity (PGV) patch and the nonlinear site response could be attributed to the soft sediment with high pore fluid pressure and low-velocity structure beneath this region. However, the greater seismic moment and closer faulting location to the thick-mudstone-layer region for the 2016 Meinong event reinforced the strong ground shaking and serious damage over the broad area. This implies that this thick-mudstone-layer region in southern Taiwan plays a crucial role in earthquake response, and an investigation of characteristic site effects should be conducted for seismic hazard mitigation.Graphic abstract

A Method to Directly EstimateS-Wave Site Amplification Factor from Horizontal-to-Vertical Spectral Ratio of Earthquakes (eHVSRs)

ABSTRACTThe main purpose of the site classification or velocity determination at a target site is to obtain or estimate the horizontal site amplification factor (HSAF) at that site during future earthquakes because HSAF would have significant effects on the strong-motion characteristics. We have been investigating various kinds of methods to delineate the S-wave velocity structures and the subsequent HSAF, as precisely as possible. After the advent of the diffuse field concept, we have derived a simple formula based on the equipartitioned energy density observed in the layered half-space for incident body waves. In this study, based on the diffuse field concept, together with the generalized spectral inversion technique (GIT), we propose a method to directly estimate the HSAF of the S-wave portion from the horizontal-to-vertical spectral ratio of earthquakes (eHVSRs). Because the vertical amplification is included in the denominator of eHVSR, it cannot be viewed as HSAF without correction. We used GIT to determine both the HSAF and the vertical site amplification factor (VSAF) simultaneously from strong-motion data observed by the networks in Japan and then deduced the log-averaged vertical amplification correction function (VACF) from VSAFs at a total of 1678 sites in which 10 or more earthquakes have been observed. The VACF without a category has a constant amplitude of about 2 in the frequency range from 1 to 15 Hz. By multiplying eHVSR by VACF, we obtained the simulated HSAF. We verified the effectiveness of this correction method using data from observation sites not used in the aforementioned averaging in the frequency range from 0.12 to 15 Hz.

Strong-Motion Characteristics and Visual Damage Assessment Around Seismic Stations in Kathmandu after the 2015 Gorkha, Nepal, Earthquake

A rapid visual damage assessment of buildings around four strong-motion seismic stations in Kathmandu Valley was carried out after the damaging Gorkha, Nepal earthquake (Mw7.8) of 25 April 2015. The waveforms of the main shock recorded at these stations were compared with the damage to buildings around the stations. The damage was found to be related to strong-motion characteristics of the earthquake. A dominance of long-period oscillation could be observed in the records. The damage to low-rise buildings in the valley was less than anticipated from an earthquake of this magnitude given that the majority of buildings were built without proper engineering consideration. The acceleration response spectra of one of the sedimentary sites show high response in the 1–2 s period range, and nearly 10% of the buildings, which were all low-rise, suffered damage around this site.

Ground Motion Parameters for the 2011 Great Japan Tohoku Earthquake

ABSTRACTThe 2011 great Japan Tohoku earthquake is not only the most devastating but also, one of the best recorded earthquakes in the history of seismology. A thorough study of strong motion characteristics of this earthquake is conducted using 20 well established ground motion parameters (GMPs). The behaviour of these parameters with fault distance and average shear wave velocity is examined and attenuation relationships are developed using the 1172 surface level strong motion records. In addition, all GMPs are categorized on a statistical basis using principal component analysis, which is further used to rate the damage potential of ground motion records.

Building Typologies Prevalent in Northern Pakistan and Their Performance during the 2015 Hindu Kush Earthquake

The M7.5 earthquake of 26 October 2015 resulted due to reverse faulting at an intermediate depth of 210 km within the northeast-trending tabular zone underneath the Hindu Kush region, with its epicenter located 45 km southwest of Jarm in Afghanistan. In Pakistan alone, the earthquake and subsequent aftershock swarm resulted in 280 fatalities, injuries to 1,770 persons, and notable damage to 109,123 buildings. A synopsis of observations is presented herein, covering details about seismotectonics, strong motion characteristics, damage statistics, and typical building failure modes. Building damage was observed to mostly concentrate in vulnerable rural and old unreinforced masonry buildings, with aspects such as complete or partial out of plane collapse of walls, collapse of roofs due to loss of seating, shear cracking in masonry walls/panels, shear and flexural damage in masonry spandrels, cracking at infill-frame interface, damage at building corners, pounding damage, toppled minarets, and damage due to ground settlement.

Spectrum-Compatible Earthquake Records and Their Influence on the Seismic Response of Reinforced Concrete Structures

Three different methodologies for the generation of spectrum-compatible records are evaluated: wavelet-based modification of seed records, seed record adjustment based on the continuous wavelet transform, and synthetic record generation in the frequency domain. It was found that the three methodologies are capable of generating compatible records with an acceptable level of match. However, the records generated using the frequency domain approach exhibit unrealistic strong motion characteristics and a tendency to induce less inelastic demand in the structures. In the case of methodologies based on modification of actual earthquake records, it was found that when the seed records are selected based on their initial compatibility with the target spectrum, the resultant compatible records not only better retain the original characteristic of the records but the variability in the structural response is reduced.

Seismic hazard assessments at Islamic Cairo, Egypt

Islamic Cairo is one of the important Islamic monumental complexes in Egypt, near the center of present-day metropolitan Cairo. The age of these buildings is up to one thousand years. Unfortunately, many of the buildings are suffering from huge mishandling that may lead to mass damage. Many buildings and masjids were partially and totally collapsed because of 12th October 1992 Cairo earthquake that took place at some 25 km from the study area with a magnitude Mw = 5.8. Henceforth, potential damage assessments there are compulsory. The deterministic and probabilistic techniques were used to predict the expected future large earthquakes' strong-motion characteristics in the study area. The current study started with compiling the available studies concerned with the distribution of the seismogenic sources and earthquake catalogs. The deterministic method is used to provide a description of the largest earthquake effect on the area of interest, while the probabilistic method, on the other hand, is used to define the uniform hazard curves at three time periods 475, 950, 2475 years. Both deterministic and probabilistic results were obtained for bedrock conditions and the resulted hazard levels were deaggregated to identify the contribution of each seismic source to the total hazard. Moreover, the results obtained show that the expected seismic activities combined with the present situation of the buildings pose high alert to rescue both the cultural heritage and expected human losses.

Strong ground motion characteristics of the 2011 Van Earthquake of Turkey: Implications of seismological aspects on engineering parameters

The October 23 2011 Van Earthquake is studied from an earthquake engineering point of view. Strong ground motion processing was performed to investigate features of the earthquake source, forward directivity effects during the rupture process as well as local site effects. Strong motion characteristics were investigated in terms of peak ground motion and spectral acceleration values. Directiviy effects were discussed in detail via elastic response spectra and wide band spectograms to see the high frequency energy distributions. Source parameters and slip distribution results of the earthquake which had been proposed by different researchers were summarized. Influence of the source parameters on structural response were shown by comparing elastic response spectra of Muradiye synthetic records which were performed by broadband strong motion simulations of the earthquake. It has been emphasized that characteristics of the earthquake rupture dynamics and their effects on structural design might be investigated from a multidisciplinary point of view. Seismotectonic calculations (e.g., slip pattern, rupture velocity) may be extended relating different engineering parameters (e.g., interstorey drifts, spectral accelerations) across different disciplines while using code based seismic design approaches. Current state of the art building codes still far from fully reflecting earthquake source related parameters into design rules. Some of those deficiencies and recent efforts to overcome these problems were also mentioned. Next generation ground motion prediction equations (GMPEs) may be incorporated with certain site categories for site effects. Likewise in the 2011 Van Earthquake, Reverse/Oblique earthquakes indicate that GMPEs need to be feasible to a wider range of magnitudes and distances in engineering practice. Due to the reverse faulting with large slip and dip angles, vertical displacements along with directivity and fault normal effects might significantly affect the engineering structures. Main reason of excessive damage in the town of Ercis can be attributed to these factors. Such effects should be considered in advance through the establishment of vertical design spectra and effects might be incorporated in the available GMPEs.

Effects of 2D small-scale sedimentary basins on strong ground motion characteristics

A lot of research on the 2D or 3D effects of large-scale basins (within several kilometers depth) have been conducted in the past. However, different 2D aspects of small-scale sedimentary basins (within tens of meters depth) remain in the developing stage. Here, an attempt is made to analyze different aspects of small-scale basins using both numerical and empirical investigations. In the first step, the 2D effects of small-scale basins on strong motion characteristics are numerically examined both in the time and frequency domains. In addition, the effects of input motion are also explained by the results of model excitation in different orthogonal directions. Then, the numerical outcomes are verified by the analysis of actual earthquake data recorded at a downhole array in the Fujisawa small basin, Japan. In the second step, since available recorded earthquake data in small basins with a clear understanding of subsurface geology are very limited, different 2D aspects of the small basin are parametrically investigated. For this purpose, extensive parametrical studies are carried out on the main features of a small basin such as slope angle, shape, infill soil properties, and basin thickness by using the finite difference numerical method. The horizontal and vertical peak ground accelerations of 2D with respect to 1D ones are defined as the horizontal and vertical aggravation factors (AGH and AGV). The AGH and AGV factors show large sensitivity to infill soil properties, shape and thickness, and small sensitivity to slope angle. The values of AGH and AGV factors vary in the range of 0.5?2 with large variations around small basin edges due to wave coupling, conversion, scattering and focusing in the vicinity of small basin edges. These cause a complicated pattern of 2D de-amplification and amplification, which mostly affect the motion in the high frequency range (>1?Hz). Finally, the outcomes provide numerical and field evidence on the 2D effects of small basins, and give some recommendations for design codes.

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.

Influence of strong motion characteristics on permanent displacement of slopes

Landslides triggered by moderate to major earthquakes are a recognized seismic hazard. Arias Intensity (I a) is a key intensity measure of the ground motion, but significant duration is widely used to define strong motion duration. We calculate Newmark’s displacements using earthquake records bracketing a broad range of Arias Intensity and significant duration employing Newmark’s rigid block method and a number of yield accelerations. Total landslide displacement increases with the increase in the energy content of the ground motion (I a) above a threshold. Such threshold may be expressed as a function of yield acceleration of the slope regardless of the ground motion characteristics. Newmark displacement decreases with increasing duration for earthquakes with similar energy content. The wide scatter in the results converges when using formal dimensional analysis. Self-similar symmetry may facilitate the assessment of the performance of slopes during earthquakes. The mathematical framework for probabilistic determination of landslides displacement may be a useful aid to estimate the likelihood of landslide hazards provided that the geotechnical properties of the slopes are known.

東北地方太平洋沖地震による地震動の特徴

東北地方太平洋沖地震で観測された強震記録の概要を紹介した。主な特徴としては，1）短周期卓越型で広域に渡る大加速度，2）地盤による相違，3）非常に長い継続時間があげられる。

Strong Motion Characteristics of the 2011 Tohoku-Oki Earthquake

The 2011 M 9.0 Tohoku-Oki earthquake is the largest earthquake that occurred in and around Japan since the beginning of the recorded history. This megathrust event initiated approximately 100km off-shore Miyagi prefecture, in northeast Japan, and its rupture extended 400-500km along the subducting Pacific plate. This is the first M 9-class earthquake that has been closely recorded by a dense seismograph network. Strong motions of this earthquake are characterized by large seismic intensities and peak ground accelerations (PGA), long durations, and wideness of the area that experienced intense shaking. The ground motions were recorded by 1223 K-NET and KiK-net stations. The PGA exceeded gravity at 20 sites; the largest PGA, of 2933 gals, was observed at the K-NET Tsukidate station (MYG004). The attenuation of the recorded peak values shows a possibility of saturating strong ground motion amplitude with the magnitude. The complex features of the accelerograms and velocity waveforms are discussed in connection with the source processes estimated using long and short period waveform data. Due to the large ground motions and tsunamis associated with this event, more than 16 thousand people were killed and more than 360 thousand houses and buildings were totally or partially destroyed. Although the tsunamis were the primary cause of damage, the strong shaking, liquefaction and landslides also brought serious destruction. However, it was reported that the damage ratios of houses and buildings directly due to shaking were not as high as for the former earthquakes having comparable seismic intensities and PGA. The recorded ground motions at most stations where the seismic intensities and PGA were large had dominant periods shorter than 0.5s and relatively poor power in the 1-2s period range which has strong influence on the damage of few-stories wooden houses. The main reason for the short-period predominance is the amplification due to the low-velocity superficial layer and can be roughly explained by empirical amplification factors for 0.1-0.5s periods. Long-period ground motions were also observed. The velocity response spectra (5% dumping) for periods of 4-20s reached around 100cm/s at many stations, mainly in the Tohoku and Kanto regions. This level may be considered not very large taking into account that the Tohoku-Oki earthquake was an M 9-class event. In the Kanto district, at epicentral distances of 300-400km, liquefaction widely occurred at the artificially reclaimed land in Tokyo and Chiba bay areas and the basin of major rivers, such as the Tone and Ara. The damage (e.g., cutoff of lifelines and differential settlement of house-basements) due to liquefaction was very severe. In this paper we summarize the strong motion characteristics associated with the M 9.0 Tohoku-Oki earthquake and review the latest results from the viewpoint of strong motions.

Improvement in the accuracy of expected seismic intensities for earthquake early warning in Japan using empirically estimated site amplification factors

The Japan Meteorological Agency (JMA) is able to process data for its earthquake early warning (EEW) procedure very quickly by employing a seismic intensity expectation method that uses simplified strong motion characteristics. To represent one of these characteristics, the site amplification factor at the seismic intensity station, JMA uses ARV (amplitude ratio of peak ground velocity at the ground surface relative to the engineering bedrock of average S-wave velocity 700 m/s) based on topographic data. As a potential substitute for the ARV, we investigated a station correction based on empirical site amplifications obtained from recent observed seismic intensity data. When estimating this station correction, we removed an effect of the abnormal seismic intensity distribution of deep subduction-zone earthquakes and applied a correction for the earthquake source term to the attenuation relation. Station corrections were obtained for 1258 stations, representing about 30% of all current seismic intensity stations. The correlation between our station corrections at the stations and the site amplification based on topographic data is weak (correlation coefficient = 0.30). The error of the expected seismic intensity was improved by 15% by replacing ARV with the station correction.

A Preliminary Study on the Near-Source Strong-Motion Characteristics of the Great 2008 Wenchuan Earthquake in China

Abstract The great 2008 Wenchuan earthquake (12 May 2008) with a moment magnitude of 7.9 and a surface-wave magnitude of 8.0 in Shichuan, China, caused unprecedented loss of human life and widespread severe damage to many types of structures. Thirty-two strong-motion records were obtained within a source distance of 300 km, and three near-source records were obtained within a source distance of 20 km. We present the preliminary results on the characteristics of the near-source records and the strong-motion aspects of this great earthquake. This earthquake may be divided into four subevents, according to the rupture time history and the final slip distribution. Three of the four subevents have large surface fault displacement, and we consider the subevents that generated the three near-source records as surface-rupture earthquakes, supported by the comparisons made to records from other surface-rupture or buried-fault earthquakes. One station recorded strong ground motions from two subevents in two well-separated time windows, and this allows us to examine the effect of earthquake parameters for each of the subevents. We find that, in the spectral period range of 0.5–2 s, the response spectra of the near-source records from the Wenchuan earthquake are significantly less than those of buried-fault earthquakes, such as the 1989 Loma Prieta earthquake and the 1994 Northridge earthquake that have a much smaller moment magnitude than the Wenchuan earthquake. In the fault-normal direction the displacement spectra at long period for the closest station are similar to those of the Lucerne record from the 1992 Landers earthquake but significantly smaller than those of the TCU052 and TCU068 records from the 1999 Chi-Chi, Taiwan, earthquake. At short and intermediate period, the near-source spectra are much larger than the design spectra in the previous version of the Chinese design code for the heavily damaged area, but they are comparable at long spectral periods.

A PROPOSAL ON HOW TO CONSTRUCT SEISMIC DAMAGE PREDICTION MODELS CONSIDERING REGIONAL VIBRATION CHARACTERISTICS OF BUILDINGS

In order to estimate the building damage during earthquakes in the future, we should perform damage prediction analysis considering both strong motion characteristics and response characteristics of buildings since we are now becoming possible to predict strong motions with sufficient accuracy. It is indicated that the damage of a building due to an earthquake is greatly influenced by the regional characteristics of buildings in addition to construction types, floor numbers, and construction ages. In this paper vibration characteristics of reinforced concrete (RC) buildings in different regions with different design levels are collected by microtremor measurements. Then we construct the damage prediction models that reflect regional differences of the acquired vibration characteristics based on the nonlinear building models proposed by Nagato and Kawase (2001). Then we use observed strong motions and synthesized Nankai earthquake waveforms as inputs to perform nonlinear response analyses. We construct vulnerability functions for four different numbers of floors, two different ages, and five different regions. We found that when we use regionally corrected models in Kochi region for the hypothesized Nankai earthquake the damage ratios will be 18% reduced on the average.

S-Wave Attenuation Characteristics beneath the Vrancea Region in Romania: New Insights from the Inversion of Ground-Motion Spectra

The S -wave attenuation characteristics beneath the Vrancea region in Romania are analyzed from the spectra (frequency range 0.5–20 Hz) of more than 850 recordings at 43 accelerometric stations of 55 intermediate-depth earthquakes ( M 4.0–7.1) that occurred in the Vrancea seismogenic zone. The method commonly chosen for this type of investigation in the case of crustal earthquakes is the generalized inversion technique (GIT) (e.g., Andrews, 1986; Castro et al. , 1990). Yet the Vrancea dataset is entirely different from common crustal datasets. Because of the strong clustering of the hypocenters within a very small focal volume, there are only few crossing ray paths from sources to receivers. As a consequence, inhomogeneities in the attenuation properties are not averaged out, which leads to unphysical results if the standard GIT approach is adopted. The problem is discussed qualitatively by performing tests with synthetic data and solved quantitatively by adapting the GIT technique in view of these peculiarities. With the optimally adapted inversion scheme, it is possible to unravel differences in the attenuation characteristics between two (or more) sets of stations. The results show that the attenuation of seismic waves is roughly comparable in the low frequency range (<4–5 Hz) but stronger by up to an order of magnitude at higher frequencies within the Carpathian mountain arc as compared with the foreland area. Modeling this strongly frequency-dependent lateral variation of seismic attenuation by a significantly lower Q beneath Vrancea (1) provides a very good fit of observed strong-motion characteristics, (2) sheds new light on the distribution of intensities of the previous strong earthquakes, (3) will have strong implications for future hazard assessment, and (4) is fully compatible with structural models from deep seismic sounding, tomography, and teleseismic attenuation.

Attenuation Relations of Strong Ground Motion in Japan Using Site Classification Based on Predominant Period

A spectral acceleration attenuation model for Japan is presented in the present study. The data set includes a very large number of strong ground-motion records up to the 2003 Off Tokach main and aftershocks. Site class terms, instead of individual site correction terms, are used. The site classes of recording stations are from a recent study on site classification for strong-motion recording stations in Japan according to a classification scheme that has been used in Japanese engineering design. The use of site class terms enables tectonic source-type effects to be identified and accounted for in the present model. The effects of a faulting mechanism for crustal earthquakes also are accounted for. For crustal and interface earthquakes, a simple form of an attenuation model (with respect to distance) is able to capture the main strong-motion characteristics and achieves unbiased estimates. For subduction slab events, a simple distance modification factor is employed to achieve plausible and unbiased predictions. The effects of source depth, tectonic source type, and faulting mechanism of crustal earthquakes are significant. The need for magnitude- squared terms is evaluated, and the use of magnitude-squared terms reduces the interevent error further.