{"id":16,"date":"2026-06-08T15:20:48","date_gmt":"2026-06-08T06:20:48","guid":{"rendered":"https:\/\/e-defense.bosai.go.jp\/geotech\/en\/wpen\/?page_id=16"},"modified":"2026-07-07T12:33:43","modified_gmt":"2026-07-07T03:33:43","slug":"background_and_objectives","status":"publish","type":"page","link":"https:\/\/e-defense.bosai.go.jp\/geotech\/en\/background_and_objectives\/","title":{"rendered":"Background and Objectives"},"content":{"rendered":"<main>\r\n    <section class=\"second background\">\r\n      <div class=\"bg\">\r\n        <h2>Background and Objectives<\/h2>\r\n      <\/div>\r\n      <div class=\"breadcrumb\">\r\n        <ul>\r\n          <li><a href=\"\/\">Home<\/a><\/li>\r\n          <li class=\"current\">Background and Objectives<\/li>\r\n        <\/ul>\r\n      <\/div>\r\n      <div class=\"inner\">\r\n        <section>\r\n          <h3>Research Background<\/h3>\r\n          <p>In recent large-scale earthquake disasters\u2014such as the 2011 Tohoku-Pacific Ocean Earthquake, the 2016 Kumamoto Earthquake, the 2023 Turkey-Syria Earthquake, and the 2024 Noto Peninsula Earthquake\u2014large-scale aftershocks have occurred frequently both before and after the mainshock. Furthermore, it is estimated that for the Nankai Trough Earthquake, which is expected to occur in the near future, the probability of another major earthquake (a subsequent earthquake) occurring within one week of the initial major earthquake is approximately 100 to 3,600 times higher than under normal conditions, suggesting that major earthquakes will occur multiple times. Many researchers have pointed out that frequent earthquakes can lead to cumulative ground deformation and building damage; however, there is currently a lack of data to verify this in detail.<\/p>\r\n          <p>Regarding the effects of multiple earthquakes on soil liquefaction, there have been confirmed cases where significant sand boils caused by liquefaction occurred not during the major mainshock itself, but during minor aftershocks following the mainshock. Furthermore, it is known that soil extensively liquefied and subjected to significant settlement during past earthquakes can liquefy again when struck by a major earthquake, even though the overall density of soil has increased (i.e., its resistance to liquefaction has improved). Various hypotheses have been proposed regarding this phenomenon, but none have yet been proven.<br>\r\n            Since building damage caused by ground damage is highly correlated with the amount of ground deformation, the accumulation of ground deformation due to multiple earthquakes is also one of the major issues that must be addressed. Fig. 1 shows a photograph of the damage around a canal in Uchinada Town, Ishikawa Prefecture, taken after the 2024 Noto Peninsula Earthquake. It is evident that liquefaction of the ground behind the retaining walls caused the walls to shift several meters toward the canal, blocking a large portion of the canal.<br>\r\n            Fig. 2 shows the damage to a residential area in the same town of Uchinada. Houses and power poles have significantly settled and tilted. Interviews with residents in this area confirmed that their homes and private vehicles continued to settle during the aftershocks. While it is possible that such extensive deformation occurred solely due to the mainshock, based on the interview results and other evidence, it can be assumed that the deformation accumulated as a result of multiple subsequent aftershocks.<\/p>\r\n          <figure><img decoding=\"async\" src=\"https:\/\/e-defense.bosai.go.jp\/geotech\/en\/wpen\/wp-content\/themes\/geotech\/assets\/img\/Fig1_BO.jpg\" alt=\"Fig. 1: Damage around the canal (Uchinada Town, Ishikawa Prefecture)\">\r\n            <figcaption>Fig. 1: Damage around the canal (Uchinada Town, Ishikawa Prefecture)<\/figcaption>\r\n          <\/figure>\r\n          <figure><img decoding=\"async\" src=\"https:\/\/e-defense.bosai.go.jp\/geotech\/en\/wpen\/wp-content\/themes\/geotech\/assets\/img\/Fig2_BO.jpg\" alt=\"Fig. 2: Damage in regidential area (Uchinada Town, Ishikawa Prefecture)\">\r\n            <figcaption>Fig. 2: Damage in regidential area (Uchinada Town, Ishikawa Prefecture)<\/figcaption>\r\n          <\/figure>\r\n          <p>Fig. 3 illustrates the relationship between multiple earthquakes, the degree of soil liquefaction, and ground deformation. When an initial earthquake occurs and soil liquefaction progresses (the degree of liquefaction increases), the stiffness of the ground decreases, leading to further ground deformation. If, following this, smaller aftershocks occur at short intervals (at time point \u2460 in the figure), the ground is subjected to seismic motion while its stiffness is still low, resulting in significant ground deformation. On the other hand, if the interval between earthquakes becomes longer (with aftershocks occurring at time point \u2461 in the figure), the degree of soil liquefaction decreases and the ground stiffness recovers, resulting in a smaller amount of ground deformation. In contrast, if the ground is evaluated as a series of individual seismic motions based on conventional design methods, there is a high risk of underestimating both the degree of liquefaction and the amount of ground deformation. Therefore, it is extremely important to reasonably assess the effects of multiple earthquakes and appropriately evaluate the risk of damage.<\/p>\r\n          <figure class=\"herf\"><img decoding=\"async\" src=\"https:\/\/e-defense.bosai.go.jp\/geotech\/en\/wpen\/wp-content\/themes\/geotech\/assets\/img\/Fig3_BO.png\" alt=\"Figure 3: Relationship between the degree of soil liquefaction and soil deformation during multiple earthquakes\">\r\n            <figcaption>Fig. 3: Relationship between the degree of soil liquefaction and soil deformation during multiple earthquakes<\/figcaption>\r\n          <\/figure>\r\n        <\/section>\r\n        <section>\r\n          <h3>Research Objectives<\/h3>\r\n          <p>In light of the background described above, the objectives of this study are as follows.<\/p>\r\n          <section>\r\n            <h4>Establishment of a method for estimating the changing ground properties over time after liquefaction<\/h4>\r\n            <p>In order to evaluate liquefaction and the resulting ground deformation under multiple earthquake events, it is necessary to quantitatively estimate the changing properties of liquefied ground over time. Following a major earthquake, seismic activity typically remains high for several weeks, and the probability of large aftershocks increases; therefore, it is particularly important to understand changes in soil properties during the period from the occurrence of a major earthquake to several weeks afterward. However, since investigations of soil that has liquefied in actual earthquakes are generally conducted only after the seismic activity has calmed down to some extent, there is a complete lack of data from the period when the probability of large aftershocks is high. In this study, the properties of soil that has been liquefied using a shake table or similar equipment will be periodically investigated to collect data that can be used to evaluate these changes over time. Furthermore, by subjecting the soil to shaking again, the re-liquefaction strength will be evaluated.<\/p>\r\n          <\/section>\r\n          <section>\r\n            <h4>Development of Health Monitoring Technologies for Ground, Underground Structures, and Evacuation Routes<\/h4>\r\n            <p>The development of wide-area disaster assessment technologies using satellite and aerial imagery is advancing rapidly, making it possible to measure widespread building collapses, road blockages caused by slope failures, and ground settlement. However, it is not possible to quantitatively assess damage to structures that cannot be identified by visual inspection, or damage to underground structures such as buried pipes that cannot be observed from the sky. Furthermore, these technologies are not suitable for responding to subsequent large-scale aftershocks, subsequent earthquakes, or secondary disasters such as tsunamis that occur within minutes to hours after the initial major earthquake. To overcome these limitations while leveraging the strengths of existing technologies, this project aims to develop methods for rapidly assessing the damage status of the ground, underground structures, and tsunami evacuation routes (the paths taken from residential areas to tsunami evacuation towers) using sensors. Key requirements for these technologies include ease of sensor installation and the ability to establish a two-way feedback loop between the assessment results and damage assessments derived from other technologies, such as satellite and aerial imagery. Furthermore, in the future, it will be possible to automatically update the parameters of urban-scale numerical analyses based on sensor-derived damage assessment results, thereby enabling real-time evaluation of the urban disaster risk changing moment by moment.<\/p>\r\n          <\/section>\r\n          <section>\r\n            <h4>Verification of Numerical Analysis Methods, Including Parameter Settings and Modeling<\/h4>\r\n            <p>It is standard practice to verify the validity and reliability of a numerical analysis method by conducting experiments on uniform soil and comparing the results with those of the numerical analysis. In doing so, soil properties are investigated in detail to set the parameters for the numerical analysis method. However, actual ground is never uniform, and it is not uncommon for detailed soil properties to be unavailable in real design projects. In this experimental study, ground investigations ranging from the design level to the research level will be conducted to verify the validity and reliability of the numerical analysis method, taking into account errors arising from parameter settings and the modeling of heterogeneous ground.<\/p>\r\n          <\/section>\r\n          <secttion>\r\n            <p>Overall picture of this research project is shown in Fig. 4.<\/p>\r\n            <figure class=\"figure\"><img decoding=\"async\" src=\"https:\/\/e-defense.bosai.go.jp\/geotech\/en\/wpen\/wp-content\/themes\/geotech\/assets\/img\/Fig4_BO.png\" alt=\"Fig. 4: Overall picture of this project\">\r\n              <figcaption>Fig. 4: Overall picture of this project<\/figcaption>\r\n            <\/figure>\r\n          <\/secttion>\r\n        <\/section>\r\n      <\/div>\r\n    <\/section>\r\n  <\/main>","protected":false},"excerpt":{"rendered":"Background and Objectives Home Background and Objectives Research Background In recent large-scale earthquake \u2026","protected":false},"author":3,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"page.php","meta":{"_acf_changed":false,"footnotes":""},"class_list":["post-16","page","type-page","status-publish","hentry"],"acf":[],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/e-defense.bosai.go.jp\/geotech\/en\/wp-json\/wp\/v2\/pages\/16","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/e-defense.bosai.go.jp\/geotech\/en\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/e-defense.bosai.go.jp\/geotech\/en\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/e-defense.bosai.go.jp\/geotech\/en\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/e-defense.bosai.go.jp\/geotech\/en\/wp-json\/wp\/v2\/comments?post=16"}],"version-history":[{"count":14,"href":"https:\/\/e-defense.bosai.go.jp\/geotech\/en\/wp-json\/wp\/v2\/pages\/16\/revisions"}],"predecessor-version":[{"id":83,"href":"https:\/\/e-defense.bosai.go.jp\/geotech\/en\/wp-json\/wp\/v2\/pages\/16\/revisions\/83"}],"wp:attachment":[{"href":"https:\/\/e-defense.bosai.go.jp\/geotech\/en\/wp-json\/wp\/v2\/media?parent=16"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}