ALBERT

Description: Using the strong ground motion dataset of M w  4.0–6.0 earthquakes in Japan from K-NET and KiK-net, we studied empirically the 5% damped spectral acceleration amplification for periods from 0.05 to 5 s at 75 seismic stations located in the Iwate–Miyagi and Niigata regions. The method of study is based on estimating the empirical site effect from the spectral ratio of observed and predicted ground motions based on the ground-motion prediction equations (GMPEs). Our results show a large amplification at most analyzed stations at periods of 0.1 s and shorter; at periods of 0.3 s and longer, large amplifications generally dominate at basin stations, but deamplifications generally dominate at mountain stations. Empirical amplification factors of spectral acceleration were used to correct the observed strong ground motion data of two crustal earthquakes: the 2008 Iwate–Miyagi Nairiku earthquake ( M w  6.9) and the 2004 Chuetsu earthquake ( M w  6.6). The site-corrected data fit better with GMPEs inferred by less standard error. We took advantage of a large body of empirical data to develop a mean empirical site-response model for each region. These empirical models are superior to models predicted from GMPEs using only V S 30 site corrections. Those relations have shown a low correlation at short periods such as 0.1 s. We also found the relations are different for the mountain and basin stations. The method is efficient for calculating site effects at observation stations where insufficient velocity structure information and a history of earthquake recordings are available.

Description: The Bam earthquake ( M w  6.5) occurred on 26 December 2003 in southeastern Iran, causing a major disaster in the city of Bam. A remarkable vertical peak ground acceleration value of 988 cm/s 2 and two horizontal pulses were recorded inside the damaged city. Previous analyses showed that the earthquake was caused by a subsurface rupture on an unknown strike-slip fault. In this study, we attempt to determine the precise fault location and source process of the 2003 Bam earthquake by performing a multiple-time-window linear waveform inversion of teleseismic and strong-motion data, both individually and jointly. We examined the general features of the fault location and the source process by analyzing the teleseismic displacement waveforms and determined the precise features and fault geometry by inverting the three components of strong-motion velocity records. The final estimate of the source process of the 2003 Bam earthquake was determined by joint inversion of the datasets. Our results show that a single fault model, characterized by the appropriate location of the hypocenter, rake angle variations, and the Rayleigh-like speed of the rupture front can satisfactorily explain the three components of the strong-motion records at BAM station.

Description: The representation theorem and the law governing the summation of random variables implies that, given that the slip amplitudes generated during an earthquake are distributed according to the Levy law, the recorded ground motions will be approximately distributed according to the Levy law. According to this formulation, the tails of the probability density functions (PDFs) of the slip and ground motion metrics are both attenuated according to a power law characterized by a single exponent, the Levy index alpha . The Levy index of the PDF of the peak ground acceleration (PGA) should be independent of the position of the seismometers, whether they are located at the ground surface or at the bottoms of the boreholes. This hypothesis is tested with ground motions recorded during the 2003 Tokachi-oki, Japan, earthquake by seismometers located at the ground surface (K-NET and KiK-net) and in the boreholes (KiK-net). For several subsets of seismometers, we compute the PDF of the PGA and the parameters of the Levy law that best fit the PDF. For PGAs recorded at the ground surface and in the boreholes, we found that the tails of PDFs of PGA decrease with power law behaviors controlled by alpha approximately 1. The analysis of the PDFs of the random variables associated with the slip spatial distribution of two source models suggests that alpha approximately 1.45, though the Cauchy law (alpha =1) provides a reasonable fit of the same PDFs.

Description: The 11 March 2011 Tohoku earthquake (05:46:24 UTC) involved a massive rupture of the plate‐boundary fault along which the Pacific plate thrusts under northeastern Honshu, Japan. It was the fourth‐largest recorded earthquake, with seismic‐moment estimates of 3–5×1022  N·m (Mw 9.0). The event produced widespread strong ground shaking in northern Honshu; in some locations ground accelerations exceeded Embedded Image. Rupture extended ∼200  km along dip, spanning the entire width of the seismogenic zone from the Japan trench to below the Honshu coastline, and the aftershock‐zone length extended ∼500  km along strike of the subduction zone. The average fault slip over the entire rupture area was ∼10  m, but some estimates indicate ∼25  m of slip located around the hypocentral region and extraordinary slip of up to 60–80 m in the shallow megathrust extending to the trench. The faulting‐generated seafloor deformation produced a devastating tsunami that resulted in 5–10‐km inundation of the coastal plains, runup of up to 40 m along the Sanriku coastline, and catastrophic failure of the backup power systems at the Fukushima Daiichi nuclear power station, which precipitated a reactor meltdown and radiation release. About 18,131 lives appear to have been lost, 2829 people are still missing, and 6194 people were injured (as reported 28 September 2012 by the Fire and Disaster Management Agency of Japan) and over a half million were displaced, mainly due to the tsunami impact on coastal towns, where tsunami heights significantly exceeded harbor tsunami walls and coastal berms. The 2011 Tohoku event is the largest earthquake known to have struck Japan, a country having a very long documented earthquake history. Seismic‐hazard assessments based on instrumentally observed and historically documented events led most researchers to expect earthquakes no larger than about M 8.5 in the region, thus the Mw 9.0 event and huge tsunami caught many by surprise. Large …

Description: The 2007 Chuetsu-oki, Japan, earthquake is the world's first major earthquake upon a source fault that extends beneath a nuclear power plant and is also characterized by difficulty determining the source fault plane. Centroid Moment Tensor solutions indicate an M (sub w) 6.6 reverse-faulting crustal earthquake with conjugate fault planes dipping to the northwest and southeast. Early results of aftershock locations suggest that either northwest-dipping plane or southeast-dipping plane can be the source fault plane of this earthquake. We carried out source inversions and empirical Green's function simulations of observed seismograms; however, they resulted in similar waveform residuals for the two fault planes. We then determined the relative locations of earthquake asperities to the hypocenter using travel-time differences of strong-motion pulses and relocated the aftershocks observed by ocean bottom seismometers deployed in the source region. These results imply that slips mainly occurred on the southeast-dipping fault plane. This implication was later confirmed by results of reflection surveys. During the earthquake, the Kashiwazaki-Kariwa nuclear power plant experienced stronger ground motions than those anticipated at the time of design. The ground motions consist of three seismic pulses that correspond to three asperities. The first and second pulses arose from rupture propagation to the plant, while the compact asperity on the distant southeast-dipping fault plane and its S-wave radiation pattern are responsible for the significant third pulse.

Description: The Bam earthquake (M (sub w) 6.5) occurred on 26 December 2003 in southeastern Iran, causing a major disaster in the city of Bam. A remarkable vertical peak ground acceleration value of 988 cm/s (super 2) and two horizontal pulses were recorded inside the damaged city. Previous analyses showed that the earthquake was caused by a subsurface rupture on an unknown strike-slip fault. In this study, we attempt to determine the precise fault location and source process of the 2003 Bam earthquake by performing a multiple-time-window linear waveform inversion of teleseismic and strong-motion data, both individually and jointly. We examined the general features of the fault location and the source process by analyzing the teleseismic displacement waveforms and determined the precise features and fault geometry by inverting the three components of strong-motion velocity records. The final estimate of the source process of the 2003 Bam earthquake was determined by joint inversion of the datasets. Our results show that a single fault model, characterized by the appropriate location of the hypocenter, rake angle variations, and the Rayleigh-like speed of the rupture front can satisfactorily explain the three components of the strong-motion records at BAM station.

Description: Strong ground motions recorded during the 2008 Wenchuan, China, earthquake (M (sub w) 7.9) have been simulated using the stochastic finite-fault method proposed by Beresnev and Atkinson (1997, 1998b). The simulations were made for two source models. Both models are based on the fault geometry that was proposed by Koketsu et al. (2008) through inversion of teleseismic body wave data. The slip distribution obtained by this inversion was used for the first source model, while a random slip distribution was used for the second source model. The performance of each source model is quantified by calculating the bias and standard deviation of response spectra predicted by each model. For the first source model, the results show overall agreement between the simulated and observed response spectra in a period range of 0.05-1 s, as well as 4-10 s, but the model overpredicts ground motions in a period range of 1-4 s. For the second source model, the model is biased over a slightly wider period range at longer periods. The performance of the stochastic model to predict observed ground motions is also compared with several empirical ground-motion models by means of statistical tools.

Description: Using the strong ground motion dataset of M (sub w) 4.0-6.0 earthquakes in Japan from K-NET and KiK-net, we studied empirically the 5% damped spectral acceleration amplification for periods from 0.05 to 5 s at 75 seismic stations located in the Iwate-Miyagi and Niigata regions. The method of study is based on estimating the empirical site effect from the spectral ratio of observed and predicted ground motions based on the ground-motion prediction equations (GMPEs). Our results show a large amplification at most analyzed stations at periods of 0.1 s and shorter; at periods of 0.3 s and longer, large amplifications generally dominate at basin stations, but deamplifications generally dominate at mountain stations. Empirical amplification factors of spectral acceleration were used to correct the observed strong ground motion data of two crustal earthquakes: the 2008 Iwate-Miyagi Nairiku earthquake (M (sub w) 6.9) and the 2004 Chuetsu earthquake (M (sub w) 6.6). The site-corrected data fit better with GMPEs inferred by less standard error. We took advantage of a large body of empirical data to develop a mean empirical site-response model for each region. These empirical models are superior to models predicted from GMPEs using only V (sub S30) site corrections. Those relations have shown a low correlation at short periods such as 0.1 s. We also found the relations are different for the mountain and basin stations. The method is efficient for calculating site effects at observation stations where insufficient velocity structure information and a history of earthquake recordings are available.