Tottori-ken Seibu Earthquake Research Articles

KiK-net日野における2000年鳥取県西部地震とその前後の地震波の伝播時間

KiK-net日野における2000年鳥取県西部地震とその前後の地震波の伝播時間

Comparison of fault gouges in the aftershock area and the non aftershock area of the 2000 Tottori-ken Seibu earthquake

Comparison of fault gouges in the aftershock area and the non aftershock area of the 2000 Tottori-ken Seibu earthquake

間隙水圧・変形連成問題への最近の取り組み 花崗岩を起源とする断層ガウジの剪断強度および水理特性

Two effects of clay enrichment in the granite-origin fault zone due to the deformation were studied: (1) it reduces frictional strength and (2) it impedes across-fault fluid flow. We sampled two natural fault rocks located in and out of the aftershock region of 2000 Tottori-ken Seibu Earthquake (Tottori, Japan) , and measured the porosity, permeability and friction coefficient for each gouge zone. Independent of the sampling location and the difference of aftershocks' activities, the deformation concentrated gouge zone showed the lowest porosity in the specimen. The pore in the gouge with the lowest porosity was dominated by smaller sized pore throat (around 10 nm) caused by the enrichment of fine-sized clay minerals, such as smectite. Sliding deformation with permeability monitoring on natural gouges, using the pore pressure oscillation method, were performed along a 30° precut surface of Berea sandstone under 100 MPa of normal stress, 30 MPa of pore water pressure and room temperature condition. The gouges having the lowest porosity showed the lowest friction coefficient and the lowest permeability in the fault rocks. Thus both the frictional and fluid flow properties of natural gouges would be controlled by the clay mineral content. The relationship between the friction coefficient and the permeability on the natural fault gouge draws a similar trend to the previous study on simulated gouges with various mixes of smectite powder and granular quartz, but the trend for the natural fault gouge indicated c.a. 0.1 lower friction than that for the previous study.

Soil H2 and CO2 Surveys at Several Active Faults in Japan

Soil H2 and CO2 surveys were carried out along seven active faults and around the aftershock region of the 2000 Tottori-ken Seibu earthquake in Japan. Diffuse CO2 effluxes were also measured along one fault and around the 2000 aftershock region. The results show highly variable H2 concentration in space and time and it seems that the maximum H2 concentration at each active fault correlates with fault activity as exemplified by the time of the latest big earthquakes. Even though observed H2 concentrations in four faults were markedly lower than those collected previously in the latter half of the 1970s, it is evident that the higher H2 concentrations in this study are due to the addition of the fault gases. Comparing the chemical composition of trapped gases (H2: 5–20% and CO2/H2: 0.5–12) in fractured rocks of drill cores bored at the Nojima fault, a soil gas sample with the highest H2 concentration showed large amounts of the trapped fault gas, diluted with atmospheric component. The profile experiment across a fracture zone at the Yamasaki fault showed higher H2 concentrations and lower CO2/H2 ratios as was observed in soil gas from the fracture zone. A few days after the 2000 Tottori-kei Seibu earthquake, no CO2 effluxes related to the occurrence of earthquakes were observed at the aftershock region. However, only above the epicenter zone, relatively high H2 concentrations in soil gases were observed.

RECONNAISSANCE REPORT ON THE 2000 TOTTORI-KEN SEIBU EARTHQUAKE

Damage done to civil structures by the 2000 Tottori-ken Seibu Earthquake was investigated. Field surveys were made from October 8-10 by eight members dispatched by the JSCE in cooperation with other researchers. Descriptions are given of the earthquake, seismic ground motion; the damage done to such civil structures as roads, road bridges, lifelines, dams, port facilities; slope failures; and public risk management. Although peak ground accelerations were extremely intensive, structural damage was not as severe as compared with the average damage caused by past earthquakes in Japan. Such disaster responses as search and rescue activities, emergency responses, disaster information communication, and victim supports are discussed.

RECONNAISSANCE REPORT ON THE 2000 TOTTORI-KEN SEIBU EARTHQUAKE

Damage done to civil structures by the 2000 Tottori-ken Seibu Earthquake was investigated. Field surveys were made from October 8-10 by eight members dispatched by the JSCE in cooperation with other researchers. Descriptions are given of the earthquake, seismic ground motion; the damage done to such civil structures as roads, road bridges, lifelines, dams, port facilities; slope failures; and public risk management. Although peak ground accelerations were extremely intensive, structural damage was not as severe as compared with the average damage caused by past earthquakes in Japan. Such disaster responses as search and rescue activities, emergency responses, disaster information communication, and victim supports are discussed.

Strong S-wave anisotropy in the aftershock region of the 2000 Tottori-ken Seibu, Japan, earthquake (Mw6.6)

Abstract The 2000 Tottori-ken Seibu earthquake (Mw6.6) occurred in Tottori prefecture, western Japan on October 6, 2000. We conducted aftershock observation and analyzed S-wave anisotropy using the aftershocks M jma2.0 to 3.5 observed at two stations near the aftershock region. The fast S-waves are polarized to almost E-W direction, which corresponds to the P-axis direction of the mainshock. The delay time of the split S-waves ranges between 20 and 100 ms. The crack density inside and outside the aftershock area is estimated from the delay time. The distribution of crack density shows a strong spatial variation and depends on the ratio of the path length inside the aftershock region against the whole path length. Assuming a uniform distribution of anisotropy inside and outside the aftershock region, the crack densities inside and outside are 0.017 and 0.007, respectively. It thus seems probable that in the aftershock region the distribution of cracks is intensive and cracks are opened due to the presence of fluids in seismogenic layers. This considerable spatial variation of anisotropy between inside and outside the aftershock region suggests that the aftershock region may have different mechanical properties from the surrounding area.

Parallel simulation of strong ground motions during recent and historical damaging earthquakes in Tokyo, Japan

The development of high-performance computing facilities such as the Earth Simulator supercomputer and the deployment of dense networks of strong ground motion instruments in Japan (K-NET and KiK-net) have made it possible to directly visualize regional seismic wave propagation during large earthquakes. Our group has developed an efficient parallel finite difference method (FDM) code for modeling the seismic wavefield and three-dimensional visualization techniques, both of which are suitable for implementation on the Earth Simulator. We will show examples of current state of the large-scale FDM simulations of seismic wave propagation by using the Earth Simulator to recast strong ground motions during damaging earthquakes in Tokyo such as the 2000 Tottori-ken Seibu ( M J 7.3) earthquake, the 1923 great Kanto earthquake ( M7.9), and the 1855 Ansei Edo ( M7) earthquake. Significant speed-up is achieved using 64–1406 processors of the Earth Simulator with good vector performance of over 40–60% of the theoretical peak speed.

The Tottori-Ken Seibu earthquake and exacerbation of asthma in adults

The aim of the study was to characterize patients at risk for exacerbations of their asthma as a result of the Tottori-Ken Seibu earthquake and to identify factors that predict exacerbation of asthma after an earthquake. A retrospective cohort study-analysis was conducted of 156 asthmatic patients, aged 18 to 89 years, who were out-patients of Tottori University Hospital and who had completely recorded their asthmatic symptoms and measured their peak expiratory flow (PEF) rates for more than one year prior to the earthquake. Seventeen (11%) patients who experienced the earthquake were identified as having an exacerbation within one month after the earthquake. Diurnal variability of PEF during the month after the earthquake was compared to values during a matched month one year previously. When factors associated with exacerbation were identified by a review of the medical case notes and the contribution of these factors to the exacerbation was determined using multivariate analysis, airflow limitation was shown to be independently associated with exacerbation after the earthquake. Acute asthma attacks are more likely to occur within the first week after the earthquake event without diurnal PEF variability. Asthma is likely to worsen after an earthquake.

Fault rocks in the aftershock area and the neighborhood of 2000 Tottori-ken Seibu earthquake

本研究では，2000年鳥取県西部地震の余震域とその周辺地域の地表踏査を行い，地質学的手法を用いて，この地域の断層系の推定を試みた．地表踏査では断層岩類の分布，密度，幅，姿勢，変位量，色相，剪断面密度などの記載を重点的に行った．調査地域に分布する断層面の姿勢は，WNW－ESE走向とNE－SW走向，高角度に卓越している．これは地形から判読されたリニアメントや地震学的に求められた震源断層モデルのNW－SE走向の姿勢とは，若干異なっている．さらに，断層岩類と玄武岩～安山岩質岩脈は，分布・姿勢に相関関係が認められる．これらの岩相境界，特に母岩である花崗岩側に，多くの破砕帯が形成されている．これらの結果より，余震域では今回の地震以前にも断層運動が繰り返し生じ，岩脈によって活動していることが推定できる．また，生成深度の異なるカタクレーサイト，断層ガウジが共に地表に存在していることからも，複数回の断層活動が生じていたことが明らかとなった．

Study of the Lifestyle Reconstruction Process by the Tottori-ken Seibu Earthquake Part 2

Study of the Lifestyle Reconstruction Process by the Tottori-ken Seibu Earthquake Part 2

アンケート調査に基づく建物の非構造部材被害と地震動強さとの関係

We conducted questionnaire surveys to examine the relation between seismic intensities and damage of various non-structural elements of RC buildings during the 2000 Tottori-ken seibu earthquake and the 2001 Geiyo earthquake. RC buildings near the earthquake observation stations were selected for our surveys. Results of our surveys indicate the following characteristics of damage of non-structural elements of buildings in the areas where the JMA instrumental seismic intensity were less than 6.0. a) Damage was mainly detected in exterior and interior walls, window glasses, ceilings and doors. Air conditioning systems, fire protection systems and elevated equipments were slightly damaged during the earthquakes, b) Many kinds of non-structural elements were damaged in the building at the seismic intensity over 5.0. c) Percentages of buildings damaged at non-structural elements increase with older buildings, d) In many cases, several non-structural elements were simultaneously damaged during the earthquake.

KiK-net伯太および日野地点の地盤構造の推定と2000年鳥取県西部地震時の基盤地震動の再評価

KiK-net伯太および日野地点の地盤構造の推定と2000年鳥取県西部地震時の基盤地震動の再評価

Cyclic strength of imperfectly saturated sands and analysis of liquefaction

The simplified method of analysis to assess liquefaction potential of a given sand deposit is briefly introduced in the first part of this paper. Then, recent advances in the laboratory testing for evaluating liquefaction resistance are described with a particular emphasis on the sand partly saturated with water. As a means to identify the degree of saturation which is applicable for both field deposits and laboratory samples, the use of the longitudinal wave (P-wave) is proposed based on a suite of data obtained from the triaxial tests in the laboratory. It is recommended that the non-destructive P-wave measurements be carried out first to determine the degree of saturation, and then the cyclic triaxial tests involving large destructive strains should be performed to determine the cyclic strength on the same sample of the sand. In order to demonstrate usefulness of the proposed approach, two sets of undisturbed samples were secured from two sites; one is located in Sakai-minato city which has suffered severe liquefaction at the time of the 2000 Tottoriken-Seibu earthquake and the other site is located in Koshigaya city, Saitama, where likelihood of liquefaction to occur in a future earthquake is of major concern. Penetration tests and in-situ velocity logging were also conducted at these two sites. By adjusting the P-wave velocity of the undisturbed samples in the laboratory so as to have the same velocity in the field, the in-situ state of saturation was reproduced in the laboratory samples. Then, the cyclic loading tests were conducted to determine the cyclic strength of intact samples. The results of the laboratory tests as above were incorporated into the simple method of liquefaction analysis described in the first section of this paper. The analysis seems to yield results which are in reasonably good agreement with what was observed at the time of the earthquake. (Communicated by Toshio SAWADA, M.J.A.)

Visualization of 3D Wave Propagation from the 2000 Tottori-ken Seibu, Japan, Earthquake: Observation and Numerical Simulation

The dense networks of strong-ground-motion instruments in Japan (K- NET and KiK-net) provide a means of direct visualization of regional wave propa- gation during large earthquakes. For the 2000 Tottori-ken Seibu earthquake (Mw 6.6) in western Japan, snapshots of ground motion, derived directly from interpolation of a large number of array observations, demonstrate clearly the nature of the source radiation and the character of the seismic wave field propagating to regional dis- tances. In western Japan the wave field from the earthquake is characterized, in most parts, by the dominance of high-frequency (0.2-5 Hz) Lg waves on three-component acceleration records and longer-period (T 10 sec) fundamental-mode Love waves in tangential displacement. The presence of strong lateral variations in the crust and upper-mantle structures, such as the low-velocity superficial layer and the high- velocity Philippine Sea plate with shallow subduction into the mantle, impose sig- nificant modifications on the regional wave field. Further insight into the nature of the seismic wave field is gained by comparison of the observations with numerical simulation for a 3D model, including sedimentary basins by an embedded submesh. A multigrid, parallel computation using a hybrid Pseudospectral/Finite Difference Method allows the inclusion of a realistic model of the source process for the 2000 Tottori-Ken Seibu earthquake. There is good agreement in the dominant features of the regional wave field propagating through the complex structure of western Japan. However, the differences between the observations and the computer simulations indicates the need for further refinement of the source and structural models. The inclusion of amplification effects for the population centers in sedimentary basins means that the modeling procedure is already suitable for estimating the main pattern of ground motion for future earthquake scenarios.

1038 日本列島の地震波動伝播と強震動の大規模数値シミュレーション

This paper presents large-scale parallel simulation of seismic wave propagation in Japan using the Earth Simulator. The seismic wavefield in 3D heterogeneous structure is calculated by solving equation of motions in elastic media by using the parallel FDM. The results of application of the parallel FDM for modeling strong ground motion from recent large earthquakes such as for the 2000 Tottori-ken seibu earthquake in Japan, and comparison between high-density seismic observations (K-NET and KiK-net), demonstrating the effectiveness of the simulation model. Therefore the model can be applied to estimate the pattern of strong ground motion damage for future earthquake scenarios.

An Investigation of Municipality-Level Emergency Responses Conducted at the 2000 Tottoriken-Seibu Earthquake

An Investigation of Municipality-Level Emergency Responses Conducted at the 2000 Tottoriken-Seibu Earthquake

CHARACTERISTICS OF THE FINE SOILS LIQUEFIED IN THE 2000 TOTTORI KEN SEIBU EARTHQUAKE

2000年鳥取県西部地震では埋立地において液状化被害が多数みられた. 特に美保湾側の埋立地でみられた噴砂のほとんどが細粒土であったことが, 今回の地震による液状化被害を特徴付けた. 本研究では, 液状化地点より噴砂を採取すると共に, 細粒土が液状化を起こした竹内工業団地と昭和町岸壁付近において, ボーリング調査および不撹乱試料の採取を行った. これらの採取試料を用いて, 噴砂と不撹乱試料の物理特性および液状化強度を比較することにより地中の液状化層を同定した. さらに, 現行の示方書により液状化強度の検討を行い, 現行の細粒分の取り扱いに対する問題点を指摘するとともに, 細粒分の混入する土に対する液状化の評価に塑性指数や粘土分含有率の導入の必要性があることを強調した.

The Influence of 3-D Structure on the Propagation of Seismic Waves Away from Earthquakes

The seismic records from significant earthquakes are profoundly affected by 3-D variations in crustal structure both in the source zone itself and in propagation to some distance. Even in structurally complex zones such as Japan and Mexico relatively coherent arrivals are found associated with different classes of propagation paths. The presence of strong lateral variations can disrupt the arrivals, and impose significant variations in propagation characteristics for different directions from the source as illustrated by observations for the 1995 Kobe and 2000 Tottori-ken Seibu earthquakes in western Japan. Such effects can be modelled in 3 dimensions using a hybrid scheme with a pseudospectral representation for horizontal coordinates and finite differences in depth. This arrangement improves parallel implementation by minimising communication costs. For a realistic 3-D model for the structure in western Japan the 3-D simulations to frequencies close to 1 Hz provide a good representation of the observations from subduction zones events such as the 1946 Nankai earthquake and the 2000 Tottori-ken Seibu earthquake. The model can therefore be used to investigate the pattern of ground motion expected for future events e.g., in current seismic gaps.

Evaluation of Disaster Response in the Tottori-Ken Seibu Earthquake, 2000: A Preliminary Approach Using the Utstein Template

Evaluation of Disaster Response in the Tottori-Ken Seibu Earthquake, 2000: A Preliminary Approach Using the Utstein Template