Iwate-Miyagi Nairiku Earthquake Research Articles

Polarimetric Decomposition Analysis of ALOS PALSAR Observation Data before and after a Landslide Event

Radar scattering mechanisms over landslide areas were studied using representative full polarimetric parameters: Freeman–Durden decomposition, and eigenvalue–eigenvector decomposition. Full polarimetric ALOS (Advanced Land Observation Satellite) PALSAR (Phased Array type L-band Synthetic Aperture Radar) datasets were used to examine landslides caused by the 2008 Iwate-Miyagi Nairiku Earthquake in northern Japan. The Freeman–Durden decomposition indicates that areas affected by large-scale landslides show dominance of the surface scattering component in both ascending and descending orbit data. The polarimetric parameters of eigenvalue–eigenvector decomposition, such as entropy, anisotropy, and alpha angle, were also computed over the landslide areas. Unsupervised classification based on the H- plane explicitly distinguishes landslide areas from others such as forest, water, and snow-covered areas, but does not perform well for farmland. A landslide area is difficult to recognize from a single-polarization image, whereas it is clearly extracted on the full polarimetric data obtained after the earthquake. From these results, we conclude that 30-m resolution full polarimetric data are more useful than 10-m resolution single-polarization PALSAR data in classifying land coverage, and are better suited to detect landslide areas. Additional information, such as pre-landslide imagery, is needed to distinguish landslide areas from farmland or bare soil.

On the ULF magnetic ratio increase before the 2008 Iwate–Miyagi Nairiku earthquake by

Hirano and Hattori (2011), hereafter cited as H&H, report the observation of anomalous increases in the ULF geomagnetic field spectral density ratio which the authors claim to be possible precursors of the 2008 Iwate–Miyagi Nairiku earthquake. Here the results of H&H are reviewed taking into account the global geomagnetic activity level by means of ∑Kp index. This paper cast serious doubts on the seismogenic origin of the magnetic signatures documented by H&H showing that the anomalous signals are normal ULF magnetic variations induced by solar–terrestrial interaction. In summary, H&H’s claims that magnetic field disturbances about a month before the Mw 6.9 Iwate–Miyagi Nairiku earthquake on June 13, 2008 are precursors to the earthquake are unlikely to be correct.

A numerical study on the effect of shear resistance on the landslide by Discontinuous Deformation Analysis (DDA)

Japan is located in Circum-Pacific earthquake zone, which is one of the most seismologically active areas in the world. As a result, landslides have occurred frequently and often cause serious damage not only to human lives but also to the various important structures such as national roads, railway, electric power plans etc. From the engineering point of view, to investigate the mechanism of landslide due to earthquakes and estimate the damage caused by landslides are important issues. In this study, as the first step, to check the validity of DDA simulation for the seismic problems, a series of shaking table tests were carried out in the laboratory and simulated by DDA. Then, one of the largest landslides occurred in Aratozawa Area, Miyagi, Japan in 2008 caused by Iwate-Miyagi Nairiku Earthquake was simulated using DDA and discussed the mechanisms of the landslide. The 2-D DDA model for one of the survey lines was created based on the geological survey, and physical properties were determined from the laboratory tests using rock/soil samples obtained from the landslide site. In this study, to discuss the mechanism of the landslide, a series of parametric study in terms of shear resistance along the fractures was conducted.

High-resolution DEMs in the study of rainfall- and earthquake-induced landslides: Use of a variable window size method in digital terrain analysis

We undertake digital terrain analyses of rainfall- and earthquake-induced landslides in Japan, using high-resolution orthoimagery and Light Detection and Ranging (LiDAR) DEMs. Our aims are twofold: to demonstrate an effective method for dealing with high-resolution DEMs, which are often too detailed for landslide assessments, and to evaluate the topographic differences between rainfall- and earthquake-induced landslides. The study areas include the Izumozaki (1961 and 2004 heavy rainfalls), Niihama (2004 heavy rainfalls), Houfu (2009 heavy rainfalls), and Hanokidachi/Kurikoma-dam regions (the 2008M 7.2 Iwate–Miyagi Nairiku earthquake). The study areas include 7,106 landslides in these five regions. We use two topographic attributes (the slope gradient and the Laplacian) calculated from DEMs in varying window sizes. The hit rates for statistical prediction of landslide cells through discriminant analyses are calculated using the two topographic attributes as explanatory variables, and the landslide inventory data as the dependent variable. In cases of surface failure, the hit rates are found to diminish when the window size of the topographic attributes is too large or too small, indicating that an optimal scale factor is key in assessing shallow landslides. The representative window sizes are approximately 30m for shallow landslides; the optimal window size may be directly related to the average size of landslides in each region. We also find a stark contrast between rainfall- and earthquake-induced landslides. Rainfall-induced landslides are always most common at a slope gradient of 30°, but the frequency of earthquake-induced landslides increases exponentially with slope gradient. We find that the Laplacian, i.e., the attributes of surface convexity and concavity, and the slope gradient are both important factors for rainfall-induced landslides, whereas earthquake-induced landslides are influenced mainly by slope steepness.

Volcanic mountain area disaster caused by the Iwate–Miyagi Nairiku Earthquake of 2008, Japan

We conducted an investigation of the geotechnical damage caused by an earthquake that struck on June 14, 2008. The earthquake was of magnitude 7.2 and hit a volcanic mountain area in Northern Japan. During the earthquake, the largest strong motion ever, over 4G, was recorded at the ground surface in the source region. As a result of the earthquake, a landslide of 1.5millionm3 was generated near the top of the mountain and became a mud flow, traveling about 10km downstream. The geomorphic characteristics of the mud flow are reported in this paper. Another huge landslide was generated upstream near the Aratosawa Dam. It was about 1km in length, about 700m in width and had a sliding mass volume of about 67millionm3, which slipped about 320m. The geological features, the time series of the slide and the cause of the slide are also discussed. In addition, more than 50 landslide dams, formed due to the collapsed soil and rock, appeared after the earthquake. In this paper, the geotechnical properties of all the damage are introduced.

Surface faulting history of the northernmost part of the surface rupture associated with the 2008 Iwate-Miyagi Nairiku earthquake, inferred from pit excavations across the uphill-facing fault scarp

Surface faulting history of the northernmost part of the surface rupture associated with the 2008 Iwate-Miyagi Nairiku earthquake, inferred from pit excavations across the uphill-facing fault scarp

Geotechnical characteristics of collapsed slope triggered by the 2008 Iwate-Miyagi Nairiku earthquake in the Koei district, Kurihara City, Miyagi Prefecture, Japan

Geotechnical characteristics of collapsed slope triggered by the 2008 Iwate-Miyagi Nairiku earthquake in the Koei district, Kurihara City, Miyagi Prefecture, Japan

ALOS/PALSAR full polarimetric observations of the Iwate–Miyagi Nairiku earthquake of 2008

We analysed Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) data on the areas damaged by the Iwate–Miyagi Nairiku earthquake that struck Japan in 2008. The observations before and after the earthquake have been carried out in the full polarimetric mode. We observed the dominance of surface scattering of the three-component scattering model in the landslide areas and identified 11 of the 13 landslide areas. However, we also detected vacant pieces of land, pastures and other land bodies. The possible landslide areas are estimated for 102 patch areas, of which 36 correspond to the actual landslide areas. This method is useful to detect the landslide area when the land classification map or optical image taken before a disaster is available. We propose the use of σ0 VH information to distinguish the landslide areas from the other areas. Since σ0 VH is sensitive to the surface roughness of an area, vacant pieces of land and pastures, which have a relatively low surface roughness, can be distinguished from the landslide areas, which have a high surface roughness. By combining the surface scattering and the σ0 VH filter, the number of possible landslide areas is reduced from 102 to 54, which include the actual landslide areas except for some small patch areas.

Precise aftershock distribution and crustal structure in and around the northern focal area of the 2008 Iwate-Miyagi Nairiku Earthquake

The 2008 Iwate-Miyagi Nairiku Earthquake (Mj 7.2) occurred on June 14, 2008, at the eastern flank of the Ou backbone range, in the central part of northern Honshu, Japan. In the northern part of the focal area, seismic reflection/refraction experiments conducted in 2006 and 2007 revealed a series of west-dipping faults. To investigate the relation between these faults and aftershocks, we conducted a high-density seismic array observation across the northern focal area. The arrival times of earthquakes were used in a joint inversion for earthquake locations and velocity structure. The V p structure shows tilted blocks and the block boundaries coincide with the revealed west-dipping faults. These faults were interpreted to have formed during the Miocene extension. The aftershock distribution shows a concentration on a plane dipping westward approximately 40° beneath the eastern margin of the Ou backbone range. The zone of aftershock concentration can be correlated to the known range-bounding fault inferred from seismic profiling and does not coincide with the known active reverse fault (Dedana fault). These results indicate the significance of the potential source fault located along the boundary of the Ou backbone range.

Developing a Prototype Earthquake Early Warning System in the Beijing Capital Region

The Beijing capital region (36°N–42°N, 113.5°E–120°E) is located in northern China and includes Beijing City, Tianjin City, and Hebei Province. This region of critical economic and cultural importance is threatened by large earthquakes. Historical earthquake records show that this region has been struck by many strong-to-great earthquakes (see Figure 1), with magnitudes up to M 8 (the 1679 Sanhe-Pinggu earthquake). In the 20th century, the 1976 M 7.8 Tangshan earthquake caused more than 240,000 fatalities and uncountable economic losses. Developing an earthquake early warning system (EEWS) in this region is therefore of great importance and necessity. This necessity was dramatically highlighted by the disastrous Wenchuan earthquake in 2008. After the Wenchuan earthquake, a news media report that Japanese seismologists could “predict” an earthquake several seconds before its occurrence caused a lot of discussion in China. This was actually a misunderstanding of the EEWS performance during the Iwate-Miyagi Nairiku earthquake on 14 June 2008, about one month after the Wenchuan earthquake, but the importance of EEWS in earthquake disaster mitigation has become more and more evident. Accordingly, the China Earthquake Administration (CEA) was motivated to configure a nationwide EEWS. EEW systems have recently been developed in many countries and regions, such as Japan (Nakamura 1988, 1996, 2004; Horiuchi et al. 2005; Nakamura and Saita 2007; Hoshiba et al. 2008; Brown et al. 2009; Kamigaichi et al. 2009), southern California (Allen and Kanamori 2003; Wu et al. 2007; Bose et al. 2008; Allen, Brown et al. 2009; Bose et al. 2009; Cua et al. 2009; Kohler et al. 2009), Mexico (Espinosa-Aranda et al. 1995; Goltz and Flores 1997; Espinosa-Aranda et al. 2009; Suarez et al. 2009), Taiwan (Wu and Teng 2002; Hsiao et al. 2009 …

Nonlinear Earthquake Response Characteristics of a Central Clay Core Rockfill Dam

The effect of the 2008 Iwate-Miyagi Nairiku earthquake (MJ 7.2), Japan on the Aratozawa dam, which is a 74.4 m high rockfill dam with a central clay core located in the area, was studied with a main focus on the change in the vibration period, shear wave velocity, shear modulus, and pore-water pressure. In a vertical section of the central part of the dam, three sets of 3-component accelerometers and 15 pore water pressure meters were installed. During the main shock, the acceleration exceeded 10 m/s2 at the gallery, inducing large shear strains in excess of 10-3 and a sudden build-up of the excess pore water pressure in the core. Due to the large strains, the shear wave velocity and shear modulus showed a significant decrease from their initial values and the vibration period was elongated. The decreased shear wave velocity gradually recovered toward the end of the main shock, and continued to recover with the passage of time. The full recovery of the wave velocity was found to take at least one year, while the dissipation of the excess pore water pressure proceeded more quickly than the recovery of the wave velocity.

2008 年岩手・宮城内陸地震の地質構造規制

2008 年岩手・宮城内陸地震の地質構造規制

Direct magnetic signals from earthquake rupturing: Iwate-Miyagi earthquake of M 7.2, Japan

The key point of this paper is that for the first time we successfully observed “co-rupturing” Earth's magnetic field changes due to the piezomagnetic effect caused by earthquake rupturing. Electromagnetic changes associated with earthquakes have been investigated previously. Most of them are “coseismic” step-like offsets in the geomagnetic field, which are regarded as the piezomagnetic effect caused by the total static stress changes resulting from an earthquake. Proton precession magnetometers have so far been mainly used to detect seismomagnetic effects, for which the measurement interval was usually 1 or 10 min and the measurement accuracy was 0.1 nT. For seismomagnetic observations we employed flux-gate magnetometers whose specifications are the measurement with accuracy of 0.01 nT and with the sampling interval of 0.5 or 1 s. By virtue of such highly sensitive magnetometers, we show observations of magnetic signals accompanying fault movement. Our observation site happened to be situated at an epicentral distance of 26 km from the 2008 Iwate-Miyagi Nairiku earthquake of M 7.2, in NE Japan. Magnetic field components began to change almost simultaneously with the onset of the earthquake rupture and grew non-linearly until the first P wave arrival. Such magnetic signals are most probably generated by the changing stress field due to rupturing, i.e. the piezomagnetic effect, rather than the seismic dynamo effect or electromagnetic induction within the conducting crust, because they lack oscillatory features like seismic waves. We attempt to interpret the observations with the aid of quasi-static piezomagnetic-model calculation which strongly supported our observation results.

Is it possible to trace an impending earthquake's occurrence from seismo-ionospheric disturbance using principal component analysis? A study of Japan's Iwate–Miyagi Nairiku earthquake on 13 June 2008

This research uses principal component analysis (PCA) to investigate global ionospheric integrated electron content map (GIM) anomalies corresponding to Japan's Iwate–Miyagi Nairiku earthquake of 13 June 2008 (UTC) ( M w =6.9). The PCA transform is applied to GIMs for 20:00–22:00 on 08, 11, and 12 June 2008 (UTC). To perform the transform, image processing is used to subdivide the GIMs into 100 (36° longitude and 18° latitude) smaller maps to form transform matrices of dimension 2×1. The transform allows principal eigenvalues to be assigned to ionospheric integrated electron content anomalies. Anomalies are represented by large principal eigenvalues (i.e., >0.5 in a normalized set). The possibility of geomagnetic storms and solar flare activity affecting the results is done through examining the Dst index for the corresponding days. The study shows that for the Iwate–Miyagi Nairiku earthquake, PCA possibly determined earthquake-related ionospheric disturbances for the whole region, including the epicenter.

Seismo-ionospheric disturbance using principal component analysis — A study of Japan’s Iwate-Miyagi Nairiku earthquake on 13 June 2008

This research uses Principal Component Analysis (PCA) to investigate global ionospheric integrated electron content map (GIM) anomalies corresponding to Japan’s Iwate-Miyagi Nairiku earthquake on 13 June 2008 (UT) (Mj = 7.2, JMA scale). The PCA transform is applied to GIMs for 20:00 to 22:00 on June 08, 11 and 12, 2008 (UT). To perform the transform, image processing is used to subdivide the GIMs into 100 (36° long. and 18° lat.) smaller maps to form transform matrices of dimensions 2 × 1. The transform allows for principal eigenvalues to be assigned to ionospheric integrated electron content anomalies. Anomalies are represented by large principal eigenvalues (i.e., >0.5 in a normalized set). The possibility of geomagnetic storms and solar flare activity affecting the results is done through examining the Dst index for corresponding days. The study shows that for the Iwate-Miyagi Nairiku earthquake, PCA possibly determined earthquake related ionospheric disturbances for the whole region, including the epi...

A new algorithm for the detection of seismic quiescence: introduction of the RTM algorithm, a modified RTL algorithm

There are a number of reports on seismic quiescence phenomena before large earthquakes. The RTL algorithm is a weighted coefficient statistical method that takes into account the magnitude, occurrence time, and place of earthquake when seismicity pattern changes before large earthquakes are being investigated. However, we consider the original RTL algorithm to be overweighted on distance. In this paper, we introduce a modified RTL algorithm, called the RTM algorithm, and apply it to three large earthquakes in Japan, namely, the Hyogo-ken Nanbu earthquake in 1995 (MJMA7.3), the Noto Hanto earthquake in 2007 (MJMA 6.9), and the Iwate-Miyagi Nairiku earthquake in 2008 (MJMA 7.2), as test cases. Because this algorithm uses several parameters to characterize the weighted coefficients, multiparameter sets have to be prepared for the tests. The results show that the RTM algorithm is more sensitive than the RTL algorithm to seismic quiescence phenomena. This paper represents the first step in a series of future analyses of seismic quiescence phenomena using the RTM algorithm. At this moment, whole surveyed parameters are empirically selected for use in the method. We have to consider the physical meaning of the “best fit” parameter, such as the relation of ACFS, among others, in future analyses.

Preliminary Analysis for Ground Structure around Source Region of 2008 Iwate-Miyagi Nairiku Earthquake

Preliminary Analysis for Ground Structure around Source Region of 2008 Iwate-Miyagi Nairiku Earthquake

The Effect of Seismic Response Characteristics of Subsurface Ground to Damage of Low-rise RC Building in the Iwate-Miyagi Nairiku Earthquake in 2008

2008年岩手・宮城内陸地震において、ほぼ同年代に建設されたほぼ同じ構造形式を持つ3つの小学校校舎の被災程度に大きな差があったことを、主に表層地盤の地震応答特性の違いから検討した。地震後に実施した常時微動観測、余震観測の記録分析から、唯一大きな被害のあった上野目小学校周辺の地盤は他2校に比べて建物の固有周期に近い周期帯で地震動が増幅することがわかった。また、上野目小学校の敷地には切土・盛土境界が含まれていることが推測され、盛土地盤の影響を考慮した地盤の等価線形解析及び、その結果を反映した建物の非線形地震応答解析からは、上野目小学校の地震被害の程度を説明するには、盛土地盤の非線形化による地震動の増幅を考慮する必要があることを指摘した。

Rocking Motion of Structures under Earthquakes (Overturning of 2-DOF System)

In recent years, huge earthquakes happen, for example, The South Hyogo prefecture Earthquake in 1995, The Mid Niigata Prefecture Earthquake in 2004, The Iwate-Miyagi Nairiku Earthquake in 2008. In The Niigataken Chuetsu-oki Earthquake in 2007, hundreds of drums fell down and water spilled out. A lot of studies about rocking behavior of rigid body had been performed from 1960's. However, these studies were only for a specific condition of the structure size or input vibration characteristics. Therefore, generalizes fall condition for earthquake is required. This paper deals with the analytical and the experimental study of the rocking vibration of 1-DOF rocking system, 2-DOF vibration-rocking system and 2-DOF rocking system under earthquakes. In this study, the equation of motion for each rocking systems are developed. The numerical model of 2-DOF rocking system is evaluated by free rocking experiment. In this paper, “Overturning Map” which can distinguish whether structures falls or not is proposed. The overturning map of each rocking systems excited by the artificial earthquake wave calculated from the design spectrum is shown. As the result, overturning condition of structures is clarified.

Evaluation of Fourier and Response Spectra at Ichihasama and Koromogawa Seismic Intensity Observation Sites During the Iwate-Miyagi Nairiku Earthquake in 2008

本論文では2008年岩手・宮城内陸地震において震度6強を観測しながら、地震波形が現存していない一迫、衣川震度観測点の加速度フーリエスペクトルと加速度応答スペクトルを推定した。まず、マグニチュード6～7クラスの地殻内地震で得られた地震観測記録を用い、最大加速度、計測震度、地震動スペクトルの卓越周期によって加速度フーリエスペクトルと加速度応答スペクトルの推定式を求めた。続いて、推定式を求める際のデータに含まれていない自治体観測点に対して、加速度フーリエスペクトルと加速度応答スペクトルを推定したところ、観測値と概ね対応した。最後に一迫、衣川観測点の加速度フーリエスペクトルと加速度応答スペクトルを推定したところ、周期1秒以下の短周期成分が卓越することが明らかになった。