Osamu+KUSAKABE

Abstract：After the Great East Japan Earthquake occurred on March 11，2011，it appeared that Japan was extremely vulnerable to natural disasters and was lacked of adequate social systems for mitigating natural disastersThis paper describes the authors views on what we have learned from recent natural disasters，including the Hanshin-Awaji Earthquake in 1995，the Great East Japan Earthquake in 2011，the Kanto-Tohoku Flooding in 2015 and the Kumamoto Earthquake in 2016The paper then points out the need for socialization of disaster-related knowledge，followed by a need for the development of safety index systems for natural disasters for policy makers and decision makers to prioritize mitigation measures to be implementedThe paper also adds the authors view on what current civil engineering profession lacks for mitigating natural disasters

Keywords：natural disaster，earthquake，vulnerability，mitigation，safety index

CLC Number：P315Document Code：AArticle ID：1000-0666（2017）01-0022-07

1Lessons Learnt

11The Hanshin-Awaji Earthquake in 1995

The Northridge Earthquake occurred in California，USA，on Jan17，1994Many Japanese engineers in the fields of civil，geotechnical and earthquake engineering visited the affected areas to examine the damages and possible main causes for the damagesAnswering a question raised by a US news reporter at a site of highway bridge collapse，a Japanese bridge engineer was proudly saying that this type of complete collapse of bridge piers will never happen in Japan，because Japanese aseismic design is well advancedExactly a year later，however，the Hanshin-Awaji Earthquake occurred on Jan17，1995 and the bridge engineer witnessed the similar complete collapses of highway bridges in the city of Kobe

What we have learnt from the Hanshin-Awaji Earthquake 1995 may be summarized as follows

（1）There exists no absolute safety for buildings and infrastructures

（2）It is practically impossible to allocate an unlimited budget for constructing absolutely safe buildings and infrastructures

A viable solution under these circumstances is to adopt the concept of performance based designUsing the concept of performance matrix shown in Figure 1，a society will select a combination between the performance of structures and the risk that the society might encounter for a particular type of infrastructuresA few years after the Hanshin-Awaji Earthquake，then the Ministry of Construction，Japan，issued general principles of structural design for civil and building structures，adopting the concept of performance based design

On more technical sides，the experiences of the collapse of bridge piers triggered the rapid development of various aseismic reinforcement methods or retrofitting methods，which have been widely implemented throughout Japan

During the Hanshin-Awaji Earthquake，several river dikes collapsed mainly due to liquefactionSince January was not considered to be a typical season of typhoon in Japan，restoration works for the failed river dikes were not considered to be extremely urgent at that timeRecent climate change，however，has led us to change our attitude for a possible combined disaster between earthquake and water-related disasters such as flooding or high tideFigure 1An example of Performance Matrix12The Great East Japan Earthquake in 2011

The Great East Japan Earthquake in 2011 occurred on March 11 differs from the Hanshin-Awaji Earthquake in many waysThe Hanshin-Awaji Earthquake is an active fault type of earthquake located directly above the focus，while the Great East Japan Earthquake is a trench type earthquake occurred in a subduction zoneThus the duration of the earthquake motions is much longer and the scale of affected areas is much wider for the Great East Japan EarthquakeMore importantly，trench type earthquakes are usually associated with tsunami disasterConsequently the damages caused by the Great East Japan Earthquake are much more significant and extend a much wider region，requiring a long period of restoration works

What we have learnt from the Great East Japan Earthquake are summarized in a document published by the Japan Geotechnical Society（2011）Japan Geotechnical Society2011Ge-hazards during earthquakes and mitigation measures–Lesson and recommendation for the 2011 Great East Japan Earthquakeentitled “Gehazards during earthquakes and mitigation measures–Lesson and recommendation for the 2011 Great East Japan Earthquake”

Some of the important points which the author pointed out in the above publication are as follows，together with a few additional points

（1）Significance of subduction zone earthquakeUnlike earthquake caused by inland active faults，such as the 1995 Hanshin-Awaji Earthquake，the Great East Japan Earthquake is an earthquake along the subduction zone of a large moment magnitude of MW90，whose seismic motions continued for a long timeDamage from this earthquake and its many aftershocks occurred in many locations over a very wide area，causing restoration and recovery to be delayedThe unprecedented scale of the problem was overwhelming with the immediate damage compounded by the tsunami，ground contamination，salinity of farmland and the need for dispose of the waste generated

地震研究40卷第1期Osamu KUSAKABE：A Thought：What have We Learned from Natural Disasters？ Five Years after the Great East Japan Earthquake（2）The difference in structural safety of public and private assetsDamages of many public assets such as social infrastructures that had been designed in accordance with the latest technical standards were little or none，which had proven effectiveness of the current seismic technologies，but on the other hand there was an evident lack of safety in private assets including reclaimed residential land and private houses

（3）The need for the development of technologies against gigantic tsunamiThe unprecedented power of tsunami caused significant damages in port and harbor structures as well as river dikes by in and out dynamic water pressure and erosion processesDesign and construction methods should be developed for resilient water-related structures against the tsunami attack

（4）The need for improving social systemsExperiences of the Great East Japan Earthquake have proved that technologies alone are not adequate enough for protecting society and people from natural disastersSociety itself needs to be resilient by awareness and preparedness of natural disastersThus positive disclosure for potential vulnerability of land and socialization of disaster-related technology are absolutely necessaryExperiences with natural disasters in the past have driven rapid development of disaster-related lawsTogether with reviewing the laws relating to buildings，restrictions on land use，laws guaranteeing a steady and continuous upgrade process for safer social environment should be establishedIn order to achieve this goal，social systems have to be established for making social consensus and decision making processes to allocate enough budget for mitigating disasters，together with the development of a safety index of the areas to be of use for decision makersQualified engineers in disaster-related fields play a vital role in this contextThe Japanese Geotechnical Society took an initiative to create a new qualification system by forming the Japanese Association for Geotechnical Evaluation after the earthquake

13The Kanto-Tohoku Flooding in 2015

It has been a global trend that climate change progresses in a rapid rate and the frequent occurrence of water-related disasters，such as typhoon and flooding，are associated with heavy rainfall becomes common phenomena worldwideThe Kanto-Tohoku Flooding occurred in September 2015 with a record-breaking 500 mm to 600 mm intensive rainfall in a few days caused overtopping，erosion and failures of river dikes in the areas of Kanto and Tohoku region

What we have learnt from Kanto-Tohoku Flooding are as follows

（1）Because of the recent dramatic climate change，in particular，in the pattern of rainfall，current preparedness of flooding disaster is very poor both in authorities responsible for the safety of river embankment systems and in residents living in potential risk areasIn addition，most of the current river control systems cannot cope adequately with the recent intensity and total amount of rainfall

（2）The authorities responsible for river safety are immature in disseminating the potential risks and the evacuation information to local residents in the area

（3）Due to budgetary limitaion，there is an inclination to adopt software measures，rather than hardware measures，such as strengthening river dikesThis tendency results in potential risks remained unchanged

（4）Attitude of the authorities that are responsible for safety of river embankment is rather old-fashion and tend to stick to traditional design philosophy that soil materials are the best for embankment material，and hesitates in adopting more resilient materials for reinforcement such as steel，probably because of budgetary limitations

A good example was witnessed in the recovery program of Kanto and Tohoku FloodingA line of steel sheet piles were installed as a temporary structure protecting the areas of failure zones during the recovery construction until the river embankment was rebuilt using soil materialsSurprisingly，the line of the sheet pile wall was completely removed after the recovery work completedIn contrast，there is an increasing trend to use steel sheet pile wall for recovery works in the coastal levees after the Great East Japan Earthquake

14The Kumamoto Earthquake in 2016

The Kumamoto Earthquake occurred on April，2016 along two active faultsThe first shock occurred on April 14 with the moment magnitude of MW62，which had been considered to be the main shockTwo days later on April 16，the real main shock occurred with the moment magnitude of MW70，which is the similar magnitude experienced in the Hanshin-Awaji EarthquakeAnother important feature of the Kumamoto Earthquake was that strong aftershocks continuedThus the damage had been gradually accumulated caused by the pre-shock and many aftershocks，accelerating the process of the deterioration of structural integrityThe houses and structures were then subjected to the main shock，causing significant damages and total collapseThis particular phenomena posed difficulty in rescue operations as well as restoration process

On the other hand，local government and people had learnt from the previous earthquakes described above and acquired the preparedness against natural disasterThe local government took immediate actions for some restoration works which were completed in a very short period，in particular，restoration works for highway embankment as well as protection measures against water-related disastersThe failed highway embankment was restored in a few days，since the highway network is vital for maintaining secure transportation routes for rescue operation as well as for restoration worksThe recovery works of river embankment was carried out on a 24 hour basis due to great concerns for combined disasters with high tideThe area of Kumamoto prefecture had been repeatedly suffered from severe flooding due to rainfall as well as high tideThe local government was fully aware of danger for the combined disasters

2Socialization of Geotechnical EngineeringA significant number of private houses collapsed due to either soil liquefaction or landslide during earthquakes in the past earthquakesUsing soft dredged material was a quite common practice for reclamation works along coastal areasCut and fill method is a common method for developing residential land in hilly areasIn some cases，compaction efforts are not adequate for land development and the fill areas are vulnerable for landslide during earthquake

During the Great East Japan Earthquake，27000 houses were damaged due to liquefaction and more than 5000 houses in Sendai city were collapsed due to landslideAfter experiencing such damage at the time of the earthquakes，people become very sensitive about the ground conditions on which their private houses are builtVery limited information on the ground condition，however，is available as public knowledge，when people buy a piece of land for their own propertiesUnder the current law system of private ownership，individuals need to acquire an adequate knowledge and an ability to access the information and more importantly，have a system of technical professional support

To ease the situation，the Japanese Geotechnical Society took an initiative to create a system of geotechnical evaluation especially for private propertiesThe number of the qualified engineers now amounts to about 800A group of the qualified engineers now provides a technical support for the people whose houses had been damaged mainly due to ground conditions in the Kumamoto area

Basic rules of mitigating natural disasters may be summarized as below

（1）Proper use of land according to the Basic Act for LandArticle 3 clearly states that land shall be properly used according to the natural，social，economic and cultural conditions of its area

（2）Proper disclosure of potential geotechnical risks in commercial transaction should be implementLocal government often complies the data of reclamation and development of residential land which should be open to the publicIn commercial transaction of land，ground conditions with potential risks should be clearly and adequately informed

（3）Proper visibility of qualified professionals and use their expertise to evaluate ground condition

（4）Sufficient peoples literary for sciences，in particular，natural disaster–related sciences is neededCurrently only 20% of high school students learn physic and only 3% of them learn geoscience in JapanPeoples awareness against natural disaster is of essence to mitigate natural disasters

（5）Development and use of safety index for mitigating natural disaster should be noticed

3Development of Safety Index

The World Conference on Disaster Reduction in Kobe in 2005 adopted Hyogo framework for action，which clearly states the urgent need for developing vulnerability indexAn extensive literature survey indicates that the system of indicators such as World Risk Index（WRI）is widely acceptedBy modifying WRI index，an indicator named GNS（Gross National Safety for natural disasters）was developed by a group of geotechnical engineers，including the author of this paper

Risk in GNS is defined by Hazard x Exposure x VulnerabilityFive natural events are considered in the 2015 version of GNS，including earthquake，tsunami，storm surge，sediment related disaster event，and volcanic activityAn initial calculation was carried out by using various big data available open to the publicThe result of disaster risk and vulnerability was presented in the prefectural scale and in the scale of city in JapanFigure 2 shows an example of the distribution of GNS both in the prefectural scale and in smaller scalesFigure 2GNS in 2015 in prefectural scale（a）and in smaller scale（b）The authors intension is not to provide the ranking of GNS but to offer the policy and decision makers a piece of scientific information for selecting highest priority measures for mitigation in a rational manner

Since GNS is obtained by multiplying values of vulnerability and the value of exposure，the values of GNS is strongly influenced by the exposure indicator，which implies that a gradual change of population structure in areas may form an option for mitigating the natural disastersIt is impossible that occurrence of natural disaster to be null，and measures for reducing the vulnerability may require a considerable expenditureIn this context，transference of population to safer locations may become a possible option to reduce the value of GNS

Figure 3 shows vulnerability values plotted against corresponding exposure values for various prefecturesFigure 3Vulnerability values plotted against

corresponding exposure values for various

prefectures from Kusakabe et al，2017）Dotted lines indicate the mean valuesFigure 4 shows the values of various vulnerability indicators relative to the national average（indicated by a dotted circles）with respect to the hardware and software measures，respectively，for the case of Tokyo MetropolitanDoing such visualization of insufficient indicators leads to prioritization of mitigation measures，which is a beneficial merit of GNSFigure 4Various vulnerability indicators relative to the national average（Tokyo Metropolitan）4What do We Lack in the Infrastructures Development？Five years after the Great East Japan Earthquake is quite a long period of time with respect to human life-spanThe number of evacuee still remains 144，000 at the end of August，2016，although major parts of highways，railways，ports and harbors have been restoredThe recovery process from the disaster，however，seems very slow from the view of peoples living environmentWhy is the recovery process so slow，compared to the amazing rate of development in information technology？ There must be a number of reasons for that but our profession and technology in civil engineering must change our attitude that development of infrastructures takes time unlike manufactured productsOur profession and technology in civil engineering must work for accelerating the process of infrastructure development，including planning and consensus processes

In the authors view，there are two possible reasons for thisOne is slow in technology exchange and knowledge transfer among discrete disciplines Expansion of modern scientific knowledge has been supported and accelerated by the notion of reductionism advocated by Descartes in 17th centuryIn which a complex phenomenon is divided into several elements and once we understand the element，then we integrate the knowledge of these elements to understand the complex phenomenonIf we cannot understand the divided element，we further subdivide the element into several subelementsBy doing so，fragmentation process proceedsThen we start to lack of communication among various disciplinesOne of the consequences of the reductionism is fragmentation of scientific disciplines，resulting that new generation is taught not a system but elementsScience for natural disaster is multidisciplinarilyOur profession needs to communicate with other professions，including professions in social sciences

The other is slow in adopting new effective technologies to be implemented in practice，and the phenomenon similar to valley of death between research and productionThe decision makers for infrastructures have sometimes little knowledge about cutting edge technologies，and have a tendency to use conventional methods simply because there are precedentsIn contrast，engineers and researchers engaging in the development of new technology have no experience or limited knowledge about the mechanisms for decision making process and for the ways for implementation of the new technologies into practiceForum between the decision makers and the research engineers would be of vital use for improving the current situations

5Concluding Remarks

The author described his own views on what we have learned from recent natural disasters，including the Hanshin-Awaji Earthquake in 1995，the Great East Japan Earthquake in 2011，the Kanto-Tohoku Flooding in 2015 and the Kumamoto Earthquake in 2016 in this paperBased on these experiences，the author stressed the need for socialization of natural disaster-related technology，in particular，the geotechnical engineering knowledge and the need for the development of safety index systems for natural disasters for policy makers and decision makers to prioritize mitigation measures to be implementedTo accelerate the recovery process from natural disasters，importance of communication with various disciplines and establishing forum between decision makers and research engineers were suggested

References：

KUSAKADE O，KIKUMOT M，SHIMONO K，et al2017Development of Gross National Safety Index for Natural Disasters[J].Geotechnical Engineering Journal of the SEAGS &AGSSEA，48（1）