Long-period Strong Ground Motion Research Articles

Influence of low-velocity superficial layer on long-period basin-induced surface waves in eastern Osaka basin

The long-period strong ground motions with periods above 1 s have, in the case of farther or deeper earthquakes, potential to cause serious damage to structures with low eigen frequency, such as long bridges, oil tanks, or artificially damped structures, such as high-rise buildings. This work focuses on wave propagation due to the deep large earthquake representing rare deep damaging events of the region, with relatively sparse data coverage, studied for simple geological models computed by 2D finite differences. We model the wave propagation by finite differences using up-to-date 3D structural model of the Osaka basin. The strong surface waves in the region are not directly generated by these deep sources, but they originate by refraction mostly at the edges of the bedrock–sediments interface. The objective of this research is to model observed surface Love wave generated in the eastern part of the basin that propagates approximately westwards and is recorded by several surface stations. At these stations, the 3D finite-difference modeling provides a good fit with the observed surface wave in terms of waveform, amplitude, and arrival time for the most detailed 3D velocity model that contains topmost 50–250 m structure with the lowest S-wave velocities of 250 m/s. The semblance analysis of the synthetic wave field reveals that the respective synthetic surface wave is a result of interfering waves arriving in OSA and WOS stations from NE and SE directions. Performed tests reveal that such a synthetic wave field is extremely sensitive to the presence of the superficial 50—250 m thick low-velocity structure which is only a small fraction of the propagating surface wave length and occupies only part of the surface area. The ability to model the surface wave in terms of amplitude and time arrival validates the 3D structural model for long-period Osaka Bay earthquake scenario computations.Graphical

Source rupture characteristics and ground motion simulation of the southernmost Ryukyu subduction zone 31 March 2002 Mw7.1 earthquake

An Mw 7.1 Ryukyu subduction zone earthquake struck northern Taiwan in 2002. The joint source inversion result indicates that rupture mainly propagated toward the northwest and produced a significant directivity. The long-period strong ground motion observed in northern Taiwan was directly related to source rupture effects. To assess the seismic risk in Taiwan and even East Asia more generally, it is necessary to carefully consider the various types of megathrusts that occur in the southern Ryukyu subduction zone. • An Mw 7.1 Ryukyu subduction zone earthquake struck northern Taiwan in 2002. • Rupture mainly propagated toward the northwest resulted in a strong directivity. • Long-period strong ground motion was directly related to source rupture effects. • Megathrust in Ryukyu subduction needs to carefully consider to assess seismic risk. On March 31, 2002, a magnitude 7.1 earthquake occurred off the coast of eastern Taiwan. The Taipei 101 Financial Building was under construction at that time and due to extremely strong long-period shaking, two cranes on the top floor collapsed and fell to the ground, killing five people. This earthquake was caused by a rupture of the southern Ryukyu subduction zone. The result of a joint source inversion showed that the slip originated at the mid-depth subduction interface off the eastern coast and then propagated to the western fault plane with a rupture velocity of approximately 3.0 km/s. Forward ground motion simulation indicated that the main cause of the long-period strong motion in northern Taiwan was directly related to source effects, including long rupture lasting, rupture directivity and source radiation. The seismic waves were further amplified by the soft sediments in the Taipei basin which also resulted in longer vibration time in Taipei City.

Questionnaire surveys on damages at high-rise buildings and synthesized near-fault long-period strong ground motions of the 2018 Hualien, Taiwan, earthquake

Long-period pulse-like strong ground motions were recorded near the Milun fault and caused serious building damages in the Hualien City during the main shock of the 2018 Hualien, Taiwan, earthquake. In this paper, questionnaire survey on feeling of shaking, indoor damages, structural, and nonstructural damages to high-rise reinforced concrete residential buildings were analyzed by three building groups according to the positions to the Milun fault and different site conditions. Relationships between the results of questionnaire survey on building damages and characteristics of strong ground motions were studied. Furthermore, a characterized seismic source model was proposed to elucidate the generation mechanism of near-fault long-period strong ground motions. In this model, a shallow strong motion generation area (SMGA7) in the south part of Milun fault with rise-time of 2.6 s contributed to the long-period pulse-like strong ground motions. Besides, a deep SMGA (SMGA8) under the SMGA7 with rise-time of 1.2 s also contributed to the strong ground motions. Using this model, strong ground motions at the sites of buildings for questionnaire survey were synthesized. Because of the directivity effects, amplitudes of ground motions were increased from north to south along the Milun fault, which can explain the serious building damages at the buildings located at the southwest to the Milun fault. The reasons of building damages were also examined from the aspect of predominant periods of ground sites and fundamental periods of buildings, which were extracted from microtremor measurement. Damages at the buildings located on the central part of the hanging wall with relatively good site condition were the lightest for almost all the surveyed items. Pulses with period in the range of 1 s–2 s which were generated by the SMGA8 and amplified by the near surface layers are considered to be responsible for building damages.

Long-period Strong Ground Motions in the Tokyo Bay Area Observed during Moderate-magnitude Earthquakes that Occurred in the Nankai Trough

Long-period Strong Ground Motions in the Tokyo Bay Area Observed during Moderate-magnitude Earthquakes that Occurred in the Nankai Trough

Spatial Variation of Long-Period Strong Ground Motion Observed in the Kanto Plain during the 2016 Kumamoto Earthquake

Spatial Variation of Long-Period Strong Ground Motion Observed in the Kanto Plain during the 2016 Kumamoto Earthquake

Retrofit Plan Using Dampers for an Existing High-Rise Building in Tokyo Metropolitan Area Using Maximum Considered Earthquake Ground Motions Consisting of Long-Period Strong Ground Motions and Near-Fault Ground Motions

Retrofit Plan Using Dampers for an Existing High-Rise Building in Tokyo Metropolitan Area Using Maximum Considered Earthquake Ground Motions Consisting of Long-Period Strong Ground Motions and Near-Fault Ground Motions

Tsunami Simulation by Tuned Seismic Source Inversion for the Great 2011 Tohoku Earthquake

Seismic and tsunami waves were the most destructive phenomena during the 2011 Tohoku earthquake. Here we ask whether the same source model can be used to obtain equally good simulations of the observed strong ground motions and the tsunami waves. If so, we could use the same source modeling technique for predictions of both tsunami waves and strong ground motions. Long-period (20–200 s) strong ground motion data were inverted to determine the rupture process of the 2011 Tohoku earthquake. The inverted slip distribution shows that large-slip area was extended around 150 km to north and 120 km to south from hypocenter and stretched between hypocenter and the trench. We estimated two slip models: without and with additional constraints. The first relatively rough slip model reproduced short-period tsunami wave (4–5 min). Due to better constraint by data of other kind and being relatively smooth the second model reproduces long-period tsunami wave (15–25 min), as well as keeps good fit of the short-period tsunami, although short-period tsunami becomes underestimated. We used a fully nonlinear Boussinesq water wave model to model tsunami propagation, and used the results to tune the slip model. Finally, we developed a tuned slip model that combines the features of both the first and the second slip models and reproduced both the short- and long-period tsunami waves, while maintaining good fit of the seismic waveforms.

超高層RC造の長周期地震動による損傷度の簡易評価指標

超高層RC造の長周期地震動による損傷度の簡易評価指標

Strong Ground Motion Prediction Using Virtual Earthquakes

Sedimentary basins increase the damaging effects of earthquakes by trapping and amplifying seismic waves. Simulations of seismic wave propagation in sedimentary basins capture this effect; however, there exists no method to validate these results for earthquakes that have not yet occurred. We present a new approach for ground motion prediction that uses the ambient seismic field. We apply our method to a suite of magnitude 7 scenario earthquakes on the southern San Andreas fault and compare our ground motion predictions with simulations. Both methods find strong amplification and coupling of source and structure effects, but they predict substantially different shaking patterns across the Los Angeles Basin. The virtual earthquake approach provides a new approach for predicting long-period strong ground motion.

Liquid Sloshing of Oil Storage Tanks and Long-period Strong Ground Motions due to the 2001 off the Pacific Coast of Tohoku Earthquake

Liquid Sloshing of Oil Storage Tanks and Long-period Strong Ground Motions due to the 2001 off the Pacific Coast of Tohoku Earthquake

Source process of the 2011 off the Pacific coast of Tohoku Earthquake inferred from waveform inversion with long-period strong-motion records

We have investigated the rupture process of the 2011 off the Pacific coast of Tohoku Earthquake using a multi-time-window linear waveform inversion method using long-period strong-ground motion data. From the record section of the long-period motion of the 3 phases, it is indicated that the rupture process mainly consists of the 3 stages. We have assumed a single planar fault model of 468 km long in strike and 228 km wide in dip. The seismic moment of this earthquake was estimated to be 4.3 × 1022 N m (Mw 9.0). The inverted slip distribution shows a large asperity with a maximum slip of about 47 m which is located on the shallower part of the fault plane. The rupture process is divided into three stages: a first stage with moderate slip; a second stage with large and long-duration slip in the shallow part of the fault; and a third stage with relatively small and short-duration slip in the southern part of the fault. The feature of the ground motion suggested from the record section is well represented by the peak moment rate distributions, rather than the slip distributions. The rupture velocity is around 3–4 km/s in the first and third stages, while rupture progression was suspended for a while before the rupture of the asperity.

Lessons from the 2003 Tokachi-oki, Japan, earthquake for prediction of long-period strong ground motions and sloshing damage to oil storage tanks

The 2003 Tokachi-oki earthquake (Mw 8.0) in northern Japan generated large-amplitude long-period (4–8 s) ground motions in the Yufutsu sedimentary basin, causing severe damage to seven large oil storage tanks with floating roof structures because of severe sloshing of oil. The 30,000–40,000-m3 tanks having suffered the severe damage such as fires and sinking of floating roofs experienced the sloshing with large amplitudes exceeding 3 m in which the fundamental mode was predominant. The second mode of sloshing was also excited in the 110,000-m3 tanks in which their floating roofs sank into oil, indicating that the higher modes of sloshing as well as the fundamental mode should be considered in damage prediction. The strong ground motion recordings demonstrated the earthquake dependency of predominant periods and the substantial spatial variation of the long-period shaking observed within the Yufutsu basin, meaning the necessity of source- and site-specific prediction of long-period strong ground motions. The two-dimensional numerical modeling suggested the importance of detailed structures of soft near-surface sediments as well as deep basin structure for accurate prediction of long-period strong ground motions in deep sedimentary basins.

Study on long-period strong motion simulation for large-scale earthquakes

Results of long-period strong ground motion prediction for the Nankai and Tonankai earthquakes (M ~ 8) by the three-dimensional finite difference method (3DFDM) are presented. Strong motion simulation is performed for the crustal structure model that includes 3D structures of the subducting Philippine Sea plate and the Osaka sedimentary basin. The characterized asperity model describing source heterogeneity is introduced following the source model by the Central Disaster Prevention Council, Japan (CDPCJ). We simulated the worst case that the two earthquakes occur simultaneously and the other two cases of the earthquakes occurring separately. The results indicate that the sedimentary deposits of the Osaka basin significantly affect the amplification of simulated ground motion near the basin edge and that this effect depends on the direction of wave incidence. Our results demonstrate the possibility of practical simulation of wave propagation including basin induced surface waves, for earthquakes with large-scale source faults.

Control Factors of Spatial Variation of Long-Period Strong Ground Motions in the Yufutsu Sedimentary Basin, Hokkaido, during the Mw 8.0 2003 Tokachi-oki, Japan, Earthquake

We successfully reproduced important features of long-period (7 to 8 sec), large-amplitude ground motions observed in the Yufutsu basin, Hokkaido, during the M w 8.0 2003 Tokachi-oki, Japan, earthquake through numerical simulation of wave propagation. Recordings from the dense nationwide strong ground motion networks in Japan demonstrated significant spatial variation of long-period strong ground motions within the Yufutsu basin and revealed that the long-period shaking in the Tomakomai western port was the strongest of all the sites within the basin. In interpreting or predicting long-period strong ground motions in sedimentary basins, the importance of deep basin structures, such as the depth of bedrock with an S -wave velocity over 3 km/sec has been emphasized. However, the characteristics of the underground structure model of the Yufutsu basin that explain the observations indicate that thickness of near-surface (

Near-fault strong motion complexity of the 2003 Bam earthquake (Iran) and low-frequency ground motion simulation

The 2003 December 26 Bam earthquake was an intermediate size strike-slip event that occurred beneath the Bam city, causing more than 26000 fatalities. The record of the only near-fault station (Bam station) shows a clear long-period pulse in almost fault normal direction suggesting a near-fault forward directivity effect contributing to the heavy damage observed in Bam city. In this study, the long-period (0.1–1.5Hz) strong ground motions were simulated to answer some ambiguities in source parameters for fully description of the observed motion in different components at Bam station. To this end, the Hisada's kinematic model accounting for both heterogeneous source characteristics and underground geology is applied to simulate the long-period ground motion. Different source scenarios suggested by previous studies are examined and the optimum scenario that could provide the best fitting between the simulated and observed motions for different components was introduced. The slip model and asperities as well as velocity structure parameters are optimized in order to have the best possible fit between the simulated and observed velocity time histories and spectra. The good agreements between the simulated and observed low-frequency motions indicate a successful identification of source and slip parameters of the Bam earthquake and provide a good test for the simulation technique. Furthermore, the uniqueness of the identified source parameters and the slip model is further checked against the observed near- and far-field recordings of the Bam earthquake. A good agreement between the simulated and the observed waveforms provides a base for model verification and results confirmation.

2210 やや長周期地震動の発生・伝播メカニズムと地域特性(OS13 貯槽の防災と設計I)

Oil storage tanks at Tomakomai were severely damaged by liquid sloshing generated by long-period strong ground motions in the 2003 Tokachi-oki earthquake. In this report, studies on generation and propagation of long-period waves were reviewed. Furthermore, long-period ground motions at oils complex sites were predicted for expected large earthquakes in the future.

2003年十勝沖地震による周期数秒から十数秒の長周期地震動と石油タンクの被害

The 2003 Tokachi-oki, Japan, earthquake generated sloshing of liquid in large oil storage tanks with capacities over 1, 000m3 in Hokkaido and caused damage to many of them. The maximum sloshing wave heights of about 3m were observed at two tanks with natural periods of the fundamental mode of sloshing (Ts) of 7s and 5.9s in the Tomakomai western port area and at a tank (Ts=5s) in the city of Ishikari. Damage occurred in 190 large tanks in the southern part of Hokkaido. In and around the city of Tomakomai, 170 large tanks have been damaged and this corresponds to a high damage ratio of 58%. Serious damage occurred in nine tanks and eight of them concentrated in the Tomakomai western port area, where fire broke out from two tanks and floating roofs sank into the oil in seven tanks. One of the two fires was the ring fire that lasted for about 7 hours, while the other extended to the open top fire and it lasted for about 44 hours. It was long-period strong ground motion with periods from several seconds to around 10s that generated sloshing in the large tanks. In the Yufutsu plain embracing the Tomakomai area and the Ishikari plain, the shaking with a period of 7s was stronger than that in the plains in the eastern part of Hokkaido even though the latter were closer to the source region. In the plains of Yufutsu and Ishikari, the long-period strong ground motion was not confined to the Tomakomai area but distributed widely over the plains with the strongest motion observed in the area along the north-to-south axis connecting the center of the Yufutsu plain with the eastern part of the Ishikari plain. This long-period strong ground motion is presumed to be excited by the sediments reaching a thickness of 2 to 3km inside the plains. Around the Tomakomai western port, the long-lasting long-period shaking was observed with velocity responses with a damping factor of 1% keeping over 1.5m/s in a period range between 3.7 and 8.3s and with the peak value of 2.8m/s at a period of 4.8s. This peak value is about 2.5 times as large as the ground motion level that corresponds to a code established for large oil storage tanks by the Japanese fire laws. In the Tomakomai western port area, no recordings for the last three decades are larger than the ground motion level at periods of several seconds observed during the 2003 Tokachi-oki earthquake. Comparisons between the observed maximum sloshing wave heights and the observed ground motions indicate that the maximum sloshing wave heights scale with the velocity responses at Ts's. From the sloshing response analyses for the tanks in the Tomakomai area based on the observed ground motions, we found that the sloshing with the maximum wave heights of 3m and 1.3m occurred in the seriously damaged tanks with capacities of 30, 000 to 40, 000m3 (Ts-7 to 8s) and about 110, 000m3 (Ts-12s), respectively.

Prediction of Long-period Strong Ground Motion and of Liquid Sloshing of Oil Storage Tanks at Nagoya due to Tonankai Earthquake

Prediction of Long-period Strong Ground Motion and of Liquid Sloshing of Oil Storage Tanks at Nagoya due to Tonankai Earthquake

Boundary Shape Waveform Inversion for Estimating the Depth of Three-Dimensional Basin Structures

I propose a waveform inversion scheme that estimates three-dimensional basin structure, in particular, the depth of the boundary between sediment and bedrock. This study is an extension of the boundary shape waveform inversion scheme (Aoi et al. , 1995, 1997) to a three-dimensional structure. The idea is to directly parameterize the basin topography and invert it by using long-period strong ground motions including basin-induced waves and direct waves. The depth of the topography is represented by a series of model parameters and basis functions that are rectangular (boxcar) functions. By this choice of basis functions, the inversion determines the average depth of the bedrock inside rectangles with the constraint that the observation equation, which is nonlinear in the model parameters, be satisfied best in the sense of least squares. The observation equation is linearized by omitting higher-order terms and is solved iteratively by singular value decomposition. To solve this equation, sensitivity functions (differential seismograms) are required, as well as the synthetic waveforms themselves. In this study, the finite-difference method (FDM) is used to calculate waveforms. Sensitivity functions are obtained numerically by taking the difference of waveforms from perturbed and unperturbed models. The positions of the discontinuity of the medium are required to lie on, not between, the finite-difference (FD) grid points to maintain the accuracy of FD calculation. The basis functions having rectangular domain are chosen to overcome this limitation. Since the basis functions take a constant value in a particular rectangle, inside the rectangle the perturbed model is just one grid deeper than the unperturbed model. The inverted correction values of the parameters for each iteration are rounded to the nearest multiple of the grid spacing of the FD calculation. I show the formulation of the proposed scheme and demonstrate its validity by performing a numerical experiment.

231 台湾集集地震で被害を受けた石油タンク基地における長周期地震動(OS02-2 シェル構造のシミュレーションと設計(2))(OS02 シェル構造のシミュレーションと設計)

231 台湾集集地震で被害を受けた石油タンク基地における長周期地震動(OS02-2 シェル構造のシミュレーションと設計(2))(OS02 シェル構造のシミュレーションと設計)