Simulated Strong Ground Motions Research Articles

Source Model and Simulated Strong Ground Motion of the 2021 Yangbi, China Shallow Earthquake Constrained by InSAR Observations

On 21 May 2021, an Mw 6.1 earthquake, causing considerable seismic damage, occurred in Yangbi County, Yunnan Province of China. To better understand the surface deformation pattern, source characteristics, seismic effect on nearby faults, and strong ground motion, we processed the ascending and descending SAR images using the interferometric synthetic aperture radar (InSAR) technique to capture the radar line-of-sight (LOS) directional and 2.5-dimensional deformation. The source model was inverted from the LOS deformation observations. We further analyzed the Coulomb failure stress (CFS) transfer and peak ground acceleration (PGA) simulation based on the preferred source model. The results suggest that the 2021 Yangbi earthquake was dextral faulting with the maximum slip of 0.9 m on an unknown blind shallow fault, and the total geodetic moment was 1.4 × 1018 Nm (Mw 6.06). Comprehensive analysis of the CFS transfer and geological tectonics suggests that the Dian–Xibei pull-apart basin is still suffering high seismic hazards. The PGA result demonstrates that the seismic intensity of this event reached up to VIII. The entire process from InSAR deformation to source modeling and strong ground motion simulation suggests that the InSAR technique will play an important role in the assessment of earthquake disasters in the case of the shortening of the SAR imaging interval.

Simulation of strong ground motion for a potential Mw7.3 earthquake in Kopili fault zone, northeast India

In this study, we present the results of strong ground motion simulation carried out for a potential earthquake (Mw7.3) in the Kopili source zone of northeast India using the stochastic finite fault modeling technique. Prior to simulation of the potential event, the technique was validated by simulating a recorded earthquake Mw5.3, which was located close to the Nagaon district of Assam, India. The earthquake records (Mw5.3) of ten stations in the study region were analyzed, and average source parameters, namely corner frequency, seismic moment, stress drop and source radius, estimated to be 0.48 Hz, 1.44E + 24 dyne-cm, 103.4 bar and 2.7 km, respectively. While estimating the source parameters, the path attenuation parameters (Q and ko) also constrained at each seismic station. Using the constrained attenuation parameters, site amplification factors and source parameters, we simulated strong ground motion time histories for Mw5.3 event at individual sites and found them comparable with amplitude and frequency content of the respective observed records satisfactorily. The results, therefore, validated the technique used in the study. Further, the fault parameters, site amplification factors and average of the constrained attenuation parameters were used in simulation of the potential event (Mw7.3) and strong ground motion predicted for the entire northeast region (NER) at a grid interval of 0.5°. We used average values of constrained quality factor (Q) and Kappa parameter (ko) equivalent to 182f 0.95 and 0.038, respectively, in the simulation. It is apparent that the simulated PGA conditionally followed the attenuation curves of the region, and hence, we suggest developing an appropriate attenuation curve for the NER. The study reveals that the sites located up to 250 km distance away from the source zone may experience significant PGA ranging between 160 Gals and 360 Gals. The cities located within this zone, viz., Tezpur, Nagaon, Udalguri, Diphu and Bomdila, may witness strong to very strong ground shaking associated with substantial damage to buildings and other important structures in the region.

Stochastic finite-fault method controlled by the fault rupture process

We present an improved stochastic finite-fault method controlled by the fault rupture process (NNSIM) which can make the simulated strong ground motion at a broad frequency band similar to real ground motion of the Ms 7.0 Lushan earthquake by introducing the fault physical rupture process into the stochastic finite-fault method. Two obvious improvements are obtained: 1) the non-uniform time window functions produce various shape of the simulated time series instead of one single spindle shape; 2) the non-uniform stress drops and the non-uniform time window functions improve obviously simulated pseudo-spectral acceleration (PSA), especially, the low-frequency part.•We present an improved stochastic finite-fault method controlled by the fault rupture process (NNSIM) which can make the simulated strong ground motion at a broad frequency band similar to real ground motion by introducing the fault physical rupture process into the stochastic finite-fault method. Its validity was tested by the comparisons with records of Lushan earthquake.•The non-uniform time window functions produce various shape of the simulated time series instead of one single spindle shape.•The non-uniform stress drops and the non-uniform time window functions improve obviously simulated pseudo-spectral acceleration (PSA), especially, the low-frequency part.

Assessment of maximum earthquake potential of the Kopili fault zone in northeast India and strong ground motion simulation

Maximum magnitude (MM) earthquake in the Kopili fault zone of North-East India has been assessed using different approaches, which are primarily dependent on various parameters such as fault geometry, slip rate, geodetic moment rate, and convergence rate. The analyses reveal that the source zone has accumulated strain energy, during the last 72years since 1943, enough to produce a strong earthquake of magnitude≥7. On supplementing with the historical data, we conclude Mw7.3 as the maximum potential earthquake for the Kopili source zone. Such large earthquake, on its occurrence, may cause widespread significant ground shakings and damage to infrastructures in the study region. We, therefore, also simulated strong ground motion, in the form of peak ground acceleration (PGA), for the Mw7.3 potential earthquake using Empirical Green’s Function (EGF) approach for ten different sites. In the analysis, an earthquake of magnitude Mw6.5, which has been simulated using a recorded Mw5.3 earthquake, is used as Green’s Function. The two-step approach is adopted in the simulation process, as the required criteria, i.e., moment ratio of<1000 between the target potential event (Mw7.3) and the element event (Mw5.3) could not be met. We found that the cities like Tezpur, Masamari, Tumuki, Dhekiajuli, Nagaon, Bomdila, Udalguri, Seppa, Hajoi, Behali, Guwahati, and Itanagar that are located∼60–130km from the source zone may experience very strong to moderate ground shaking with PGA ranging between 0.36–0.14g. However, the cities located in the distance range of∼130 – 300km from the source, namely Jorhat, Ziro, Mokokchung, Dhubri, and Kokrajhar are expected to have low ground shaking with PGA<0.14g. The study therefore provides valuable insights to the likely seismic hazard scenario in north-east India.

High Attenuation Rate for Shallow, Small Earthquakes in Japan

We compared the attenuation characteristics of peak ground accelerations (PGAs) and velocities (PGVs) of strong motion from shallow, small earthquakes that occurred in Japan with those predicted by the equations of Si and Midorikawa (J Struct Constr Eng 523:63–70, 1999). The observed PGAs and PGVs at stations far from the seismic source decayed more rapidly than the predicted ones. The same tendencies have been reported for deep, moderate, and large earthquakes, but not for shallow, moderate, and large earthquakes. This indicates that the peak values of ground motion from shallow, small earthquakes attenuate more steeply than those from shallow, moderate or large earthquakes. To investigate the reason for this difference, we numerically simulated strong ground motion for point sources of Mw 4 and 6 earthquakes using a 2D finite difference method. The analyses of the synthetic waveforms suggested that the above differences are caused by surface waves, which are predominant at stations far from the seismic source for shallow, moderate earthquakes but not for shallow, small earthquakes. Thus, although loss due to reflection at the boundaries of the discontinuous Earth structure occurs in all shallow earthquakes, the apparent attenuation rate for a moderate or large earthquake is essentially the same as that of body waves propagating in a homogeneous medium due to the dominance of surface waves.

The First Surface‐Rupturing Earthquake in 20 Years on a HERP Active Fault is Not Characteristic: The 2014Mw 6.2 Nagano Event along the Northern Itoigawa–Shizuoka Tectonic Line

Online Material: Table of fault displacement measured at sites along the surface‐rupture zone of the 2014 Nagano earthquake. The M w 6.2 ( M w 6.7) Nagano‐ken‐hokubu earthquake (hereafter Nagano earthquake) struck northern Nagano, central Japan, on 22 November 2014, destroying more than 100 houses and injuring 46 people. The maximum peak ground acceleration of 589 Gal was recorded at K‐NET Hakuba station, located 3.3 km west of the epicenter (National Research Institute for Earth Science and Disaster Prevention, 2014). However, the areas that suffered from severe shaking, Japan Meteorological Agency (JMA) intensity 6, were limited to a few villages ∼17 km from the epicenter. The most striking feature of this earthquake is that more than 9 km of complex surface faulting occurred on the previously mapped 26‐km‐long north–northwest‐trending Kamishiro fault, one of the segments of the 150‐km‐long Itoigawa–Shizuoka tectonic line (ISTL) active fault system. This earthquake was the first surface‐breaking earthquake to occur on one of the 110 major inland active faults prioritized for evaluation by the Headquarters for Earthquake Research Promotion (HERP) that was launched in 1995 after the 1995 Kobe earthquake. A 14% probability of a large earthquake of M w∼8.3 occurring within the next 30 yrs from the entire ISTL rupture was estimated, the second highest among all the major active faults (HERP, 2014). In addition, the anticipated shaking intensities for the regions around the ISTL have been available to the public since 2005, based on simulated strong ground motion with realistic fault dimensions and fault geometry. The 2014 Nagano earthquake, as a surface‐rupturing event, gave us an opportunity to see whether our forecast, based on geologic, paleoseismic, and seismic engineering, was appropriate or whether it requires strategic improvement for seismic‐hazard assessment in Japan. In this article, we describe the surface ruptures associated with the 2014 Nagano earthquake, mostly along the …

Strong Ground Motion Simulations of theMw 7.9 Wenchuan Earthquake Using the Empirical Green’s Function Method

The M w 7.9 Wenchuan earthquake shocked China as well as the world, not only because of its great moment magnitude but also due to the terrible casualties. The complex nature of this earthquake combined with its damage brings the need for studies that assess the seismological characteristics of the M w 7.9 Wenchuan earthquake. In this study, we present the strong ground motion simulation of the great earthquake using the empirical Green’s function (EGF) method. First, we select four M w 4.9 and 5.0 aftershocks, the motions of which are used as Green’s functions. The source parameters of the aftershocks including fault size and stress drop are estimated for the simulation. Then the source model of M w 7.9 with asperities (strong‐motion generation area) is derived using forward modeling by trial and error. To validate the accuracy of the proposed source model, strong ground motions at nine stations are synthesized by the EGF method. The simulated strong ground motions are compared with the observed records in terms of acceleration waveforms, velocity waveforms, and pseudoacceleration response spectrum. Despite some discrepancy, the synthesized motions at most stations show good agreement with the observed records. In the proposed source model, the stress drop of the three asperities on the source fault is about 10 MPa, whereas the ratio of combined area to the rupture area is 0.24, which approximates 0.22 from the empirical relationship.

Influence of Uncertain Source Parameters on Strong Ground Motion Simulation with the Empirical Green's Function Method

A combined stochastic and Green's function approach was developed to simulate strong ground motions in Southwest Western Australia (SWWA) in a previous study. Although it was demonstrated that adopting the source parameters derived from other regions yielded reasonable simulation of ground motions in SWWA as compared with a few available strong motion records, the effect of source parameter variations on simulated ground motions was not known. This article performs a statistical study of the effects of random fluctuations of the seismic source parameters on simulated strong ground motions. The uncertain source parameters, i.e., stress drop ratio, rupture velocity, and rise time corresponding to the empirical source models are assumed to be the respective mean value of the parameter and normally distributed with an assumed coefficient of variation. The Rosenblueth's point estimate method [Rosenblueth, 1981] is used to calculate the statistics of the simulate ground motion parameters corresponding to different magnitudes and epicentral distances. The accuracy of the Rosenblueth's point estimate method in estimating the mean and standard deviation of ground motion PGA, PGV, and response spectrum is proven by simulating the ground motions from an ML6.0 and epicentral distance 100 km event with both the Rosenblueth's point estimate method and the Monte Carlo simulation method. A sensitivity analysis is preformed to investigate the effect of random fluctuations of each source parameters on strong ground motion simulation. A coefficient of variation model for ground motion parameters is developed based on the simulated data as a function of the variations of the three source parameters and earthquake magnitude, which can be used in probabilistic predictions of earthquake ground motions with uncertain source parameters.

Current state of integrated earthquake simulation for earthquake hazard and disaster

This paper presents the current state of integrated simulation for earthquake hazard and disaster. This simulation takes advantage of the macro–micro analysis method; this method estimates an earthquake’s strong motion with high spatial and temporal resolution, using the bounding medium theory to obtain optimistic and pessimistic estimates of expected strong motion distribution and the singular perturbation expansion that results in an efficient multi-scale analysis. Integrated earthquake simulation calculates seismic responses for all structures in a target area, inputting simulated strong ground motion to a structure analysis method that is plugged into the system by means of a wrapper; a suitable method, linear or nonlinear, is chosen depending on the type of the structure. The results of all simulations are visualized so that residences and government officials can share a common recognition of earthquake hazard and disaster. Two examples of this integrated earthquake simulations are presented; one is made by plugging nonlinear structure analysis methods into the system, and the other is made for an actual city, the computer model of which is constructed with the help of available geographical information systems.

Simulated Strong Ground Motions for the GreatM9.3 Sumatra–Andaman Earthquake of 26 December 2004

AbstractOn 26 December 2004, a devastating earthquake of M 9.3 occurred offshore northern Sumatra. Due to the size of this earthquake and the accompanying tsunami wave, disastrous consequences have been observed in several countries around the Indian Ocean. The tectonics in the region are characterized by the oblique, north-northeast-oriented subduction of the Indian–Australian plate under the Sunda microplate with a rate of 6–6.5 cm/yr. This oblique convergence results in strain partitioning, where the trench-perpendicular thrust faulting along the subducting slab accommodates the east–west component of the motion, whereas the north–south component of the motion is probably accommodated by the right-lateral strike-slip faulting along the Great Sumatran fault and the Mentawi fault. Source parameters of the 26 December 2004 event have been used for modeling the resulting ground motions in the nearby affected regions. Results give an insight on the importance of ground shaking in the total destruction of places like Banda Aceh, northern Sumatra, Indonesia. The modeling is performed for a multiasperity finite fault using a hybrid procedure combining deterministic modeling at low frequencies and semistochastic modeling at high frequencies. Results show that strong shaking was distributed over a large area including northwestern Sumatra and its offshore islands. In Banda Aceh, which experienced significant damage, bedrock velocities reached 60 cm/sec with duration of the shaking of ca. 150 sec. The largest ground motions occurred near the strongest asperities of the fault plane, where velocities of 200 cm/sec are modeled for bedrock conditions.

COMPARACIÓN DEL COMPORTAMIENTO DE EDIFICIOS EN EL VALLE DE MÉXICO ANTE SISMOS DE SUBDUCCIÓN Y DE FALLA NORMAL

Se realiza un estudio comparativo del comportamiento que presentan algunas estructuras desplantadas en distintos sitios del valle de México, mediante la aplicación de un modelo simplificado (Miranda y Taghavi, 2005) ante eventos sísmicos simulados y registrados de subducción y falla normal. Se usa el método de simulación de funciones empíricas de Green (Ordaz y otros, 1995) y los sismos utilizados son los del 25 de abril de 1989 y del 21 de julio de 2000. Se analiza el comportamiento elástico estructural considerando dos tipos de deformación lateral: como viga de flexión y como viga de cortante, y se comparan los resultados en términos de los espectros de respuesta inelásticos, de la energía de entrada y de la energía histéretica normalizada de un sistema de un grado de libertad (1GDL). Los resultados muestran que un sismo de falla normal, debido al mayor contenido de alta frecuencia, provoca que los modos superiores de la estructura tengan mayor participación, lo que origina mayores intensidades en estructuras de periodo corto. Esto podría provocar mayores daños tanto en el edificio, como en sus contenidos con respecto a un sismo de tipo subducción. Para fines prácticos, se recomienda utilizar acelerogramas de diseño tanto de sismos de subducción como de falla normal y poder así evaluar mejor la respuesta estructural y el daño que ambos podrían provocar.

Testing the Validity of Simulated Strong Ground Motion from the Dynamic Rupture of a Finite Fault, by Using Empirical Equations

This paper is concerned with testing the validity of the ground motions estimated by combining a boundary integral equation method to simulate dynamic rupture along finite faults with a finite difference method to compute the subsequent wave propagation. The validation exercise is conducted by comparing the calculated ground motions at about 100 hypothetical stations surrounding the pure strike-slip and pure reverse faults with those estimated by recent ground motion estimation equations derived by regression analysis of observed strong-motion data. The validity of the ground motions with respect to their amplitude, frequency content and duration is examined. It is found that the numerical simulation method adopted leads to ground motions that are mainly compatible with the magnitude and distance dependence modelled by empirical equations but that the choice of a low stress drop leads to ground motions that are smaller than generally observed. In addition, the scatter in the simulated ground motions, for which a laterally homogeneous crust and standard rock site were used, is of the same order as the scatter in observed motions therefore, close to the fault, variations in source propagation likely contribute a significant proportion of the scatter in observed motions in comparison with travel-path and site effects.

Strong ground motion modelling of causative fault for the 2002 Avaj earthquake, Iran

The suitability of a very fast method for obtaining synthesizing accelerograms has been demonstrated for a hybrid simulation technique of source wavelet and acceleration envelope waveform for the 2002 Avaj earthquake. This method is based on the amplitude modeled white noise and envelope waveform. The estimation of peak acceleration from a preliminary simulated record is based on using modeling parameters of rupture plane instead of empirical relations for peak acceleration. Based on comparison between observed and simulated strong ground motion data, a fair agreement is observed between simulated and observed records up to distances 40 km for peak acceleration and duration. The most important feature of the recorded strong motion is decay up to a distance of 40 km which is due to direct upgoing shear waves. At distance of 50 to 60 km peak acceleration increase, which is due to postcritical reflection from velocity gradient in the lower crust. A flat trend is observed for peak acceleration at distance of 60 to 100 km. The simulation indicates that the rupture is started at depth of 8 km and propagated from northwest to southeast. The causative fault for the 2002 Avaj earthquake shows similar mechanism to the 1962 Buin-Zahra earthquake.

実測データに基づく木造住宅の三次元非線形動的挙動解析モデルの構築

In this paper, first we measure microtremors of wooden structures to obtain their natural frequencies. Then we construct three-dimensional structure models based on experiment data, such as beam-column connections, brace-column connections, shear walls with brace and panels, and so on. Next, we compare natural frequencies from microtremors with those acquired from eigenvalue analyses of three-dimensional structure models. We construct inverted elastic models by increasing stiffness until the natural frequency matches with the observed one. Then we examine whether the models are appropriate by comparing its nonlinear behavior with the result of a full-scale shaking table test of a wooden structure. Finally we evaluate the seismic performance of the wooden structures by using earthquake observation records and simulated strong ground motions. We confirmed that the natural periods of wooden structures obtained from microtremor linearly correlate with their wall-length ratios. We also confirmed that dynamic characteristics of structure models could be tuned up to approximate those of mirotremors. Finally we confirmed that modern wooden structures that we studies here seem to have sufficient seismic performance so that they would not be collapsed or heavily damaged for strong ground motions in the near-fault regions.

統計的グリーン関数法による1993年北海道南西沖地震の震源域を含む広域における地震動シミュレーション : 強震動予測のための震源モデルの特性化手法の検証

We simulated strong ground motions during the 1993 Hokkaido-Nansei-Oki, Japan, earthquake (MJMA 7.8) based on its variable-slip rupture model and on two types of characterized asperity models to verify the characterizing procedure of source models for the strong motion prediction in future earthquakes. The asperity models were characterized by the total seismic moment, the short-period level of the source spectra, and the ratios of the area, the slip amount, and the effective stress on the asperity to those on the entire fault. The stochastic Green's function method was applied to the wide area including the epicentral region, and the following results were obtained : 1) The asperity model whose asperity was arranged at the shallow position according to the final slip distribution of the variable-slip rupture model produced a little larger ground motions than the variable-slip rupture model did. 2) On the other hand, the asperity model whose asperity was arranged at the deep position according to the short-period level distribution of the variable-slip rupture model produced the same ground motions as the variable-slip rupture model did.

経験的グリーン関数法に基づく1855年安政江戸地震の震源パラメーターと地震動の推定

The 1855 Ansei-Edo earthquake caused severe damage to Tokyo (Edo) metropolitan area. The damage was the next to that in the 1923 Kanto earthquake. In this study, source parameters of the 1855 Ansei-Edo earthquake were estimated by obtaining a good match between the simulated strong ground motions by the empirical Green's function method and the macroseismic data (isoseismal map). The hypocenter of the earthquake is most plausible near the border of Chiba and Ibaraki prefectures at a depth of 68km, near the upper surface of the Pacific plate. The magnitude of 7.4 is the best estimate for interpreting the macroseismic data.