●Messages from Departments and Centers of NILIM

Are buildings really safe enough to survive
earthquakes of “unanticipated” scale?
NISHIYAMA Isao（D.Eng.）
Director of Building Department（key words） above-expected earthquakes, buildings, seismic safety

1.

It is regrettable that we might have lost the chance

Introduction
Through its research in the fields of structures, fire

safety, environment and equipment, the Building

to carry out a careful investigation by using the term
“unexpected”.
It is undeniable, however, that the earthquake andDepartment supports building technology standardstsunami were huge. It stands to reason that people willbased on scientific and technical findings.
The subject of this article is seismic safety of

now worry if buildings are really safe enough tobuildings, and we have been playing an essential rolesurvive earthquakes of “unanticipated” (I dare to use

in setting better building technology standards. All ofthis word) scale.

us may now have a keen interest in this subject, andwe tend to ask ourselves whether we can just leave3.

things as they are or we should take further action toMagnitudeEarthquake

andTsunamiofMaximum

better prepare for mega-earthquakes which are likely

The interim report submitted by “the Experts

to occur in the future. Let me explain this subject toCommittee to Examine Measures against Earthquakesyou.

and Tsunamis Based on Lessons Taught by the 2011
off the Pacific coast of Tohoku Earthquake” formed

2. The Unexpected Great East Japan Earthquake

under the Central Disaster Prevention Council (Jun,Since the 2011 off the Pacific coast of Tohoku

2011) states “To make future assumptions concerning

Earthquake (The Great East Japan Earthquake) which

possible earthquakes and tsunamis, we should review

hit Japan in March of last year, we have often heard

the way we thought in the past and must now consider

seismologists say the word “unexpected” referring toeach and every possibility of the largest-scale

both the seismic scale and the tsunami’s destructive

earthquakes and tsunamis based on scientific findings

power.

such as sediment examinations”. They have actually

To non-specialists, this may have sounded likeput this into action by reviewing the hypocentral

something far beyond the scope of knowledge any

region and tsunami source region of the Nankai

human could have, but to skilled people with expertiseTrough. They have now taken a step forward init may not have been clearly considered at the initial

examining the use of a seismic source dislocation

design stage. It is nearly unthinkable that thismodel and a tsunami dislocation model.

knowledge.

On the other hand, institutions such as the Japan“Unexpected” may not be the type of word we should

Society of Civil Engineers or the Ministry of Land,use talking to ordinary citizens who faced a disaster ofInfrastructure, Transport and Tourism offered somethat scale.

guideposts (1) to the way of handling evacuation fromearthquake

wasbeyondhuman

●Messages from Departments and Centers of NILIM
tsunami. To prepare for the “level 1” tsunamis which

lives (“hardware-centric policy”). This posture clearlytake place once in several dozens of years to more

contradicts the Central Disaster Prevention Council’s

than a hundred years, tangible measures are to bepolicy which almost abandons relying only on the use

employed to protect human lives and properties.

of tangible facilities as the only measures to deal with

Evacuation will play a key role as an intangible

tsunami. The difference in their attitudes derives frommeasure in the case of “level 2” tsunami which is athe different ways that damages by an earthquake andlevel far beyond the application of tangible measuresby a tsunami are revealed.

stating

It is irrelevant to make a simple comparison

that dependence on “hardware-centric policy” or

between the largest scale earthquakes defined by theconstructing

anExpert Examination Committee of the Central Disasterembankment, is not economical, although it isPrevention Council and the extremely rare earthquakes

theoretically possible, with an ample budget, to build

defined by the technical standards for seismic building

independent facilities like buildings which are robust

construction, because the former assumes specificenough to withstand a “level 2” tsunami.

earthquakes and the latter does not necessarily do so.

at “level 1”. They have establishedcontinuous

a policy

facilities

suchasThe latter is also more focused on seismic ground
4. Are Buildings Really Safe Enough To Survive

motions than on the earthquake itself.

Earthquakes of “Unanticipated” Scale?
A consoling aspect of the Great East Japan
Earthquake is that direct damage to buildings by theearthquake itself was not huge (2). However, arebuildings

reallysafe

enoughtosurvive

amega-earthquake like the Nankai Trough Earthquake
which is predicted to surely come in the near future?
We have no choice but to rely on tangible facilities
to deal with seismic motion which takes place rightafter an earthquake, even a “level 2” earthquake, as wewill not have enough time for evacuation even though
the intangible measures mentioned above for tsunami
are supposed to basically be taken for “level 2”.
Technicalstandards

forseismic

building

Figure 1. Seismic Intensity of Each Region from the Great
East Japan Earthquake

construction set guidelines 30 years ago stipulating anearthquake happening on rare occasions as “level 1”,

On the other hand, what they have in common is theand one occurring on “extremely” rare occasions asfact that final judgments are always made by experts“level 2”, so the basic methodology applied here forbased on scientific and empirical information such as

tsunami is the same as that previously applied tothe past earthquake damage and observation records.

earthquake

classification.

However,technical

There is a methodological process of extrapolation,

standards for seismic building construction, even atwhereby“level 2”, demand the use of tangible measures so that

subsequent “level 2” ground motions are determinedbuildings will not collapse in order to save people’sin terms of xx year recurrence intervals using pastlargestscale

earthquakesandtheir●Messages from Departments and Centers of NILIM
observation records as statistical data. But simply

Although most buildings satisfying the current

applying numerical formula is, needless to say, an

technical standards for seismic building construction

impractical way to predict earthquakes and ground

may provide sufficient earthquake resistance against

motions of maximum magnitude which are thought tolarger than expected earthquakes, we still need to be

be barely predictable. So it is appropriate to make an

cautious about potential hazards including sympathetic

expert judgment at the present stage to makevibration of super high-rise buildings caused bycomprehensive decisions based on a combination of

long-period ground motions or liquefaction which isvarious findings and information.

susceptible to the duration of ground motion. On these

Figure 1 shows the seismic intensity caused in eachissues, we are working for measures.

region by the Great East Japan Earthquake. Most

Meanwhile, what we must not forget is that there

assessments now available concern the impacts ofare still many buildings not satisfying the current

seismic ground motion on buildings judging from eachtechnical standards for seismic building construction,of the seismic intensities, but the geographicalso called existing unqualified buildings in cities.

distribution is decided by the shortest distance fromthe hypocentral region rather than the distance from

[References]the epicenter（★）as shown on the chart.

(1) ForIn that sense, the bigger an earthquake, the larger

example,TsunamiExamination

Committee

forProtection Measures for Seashores:

the area of the hypocentral region and of the damaged

The basic rehabilitation plan for facilities such asarea. Inversely, tangible measures against groundsea embankments damaged by the 2011 off themotions may effectively deal with overly large

Pacific coast of Tohoku Earthquake. November

earthquakes on the condition that the seismic16, 2011

resistances of buildings are verified to cope with pastearthquakes which were close to the fault (inland(2) National Institute for Land and Infrastructureearthquakes, e.g. earthquakes like the 1995 GreatManagement, and Building Research InstituteHanshin-Awaji Earthquake which caused tremendous

Quick Report of the Field Survey and Researchdamage). It is a common understanding among experts

on “The 2011 off the Pacific coast of Tohoku

that the current technical standards for seismic

Earthquake” (the Great East Japan Earthquake).

building construction revealed good performance

May, 2011

during the 1995 Great Hanshin-Awaji Earthquake,
which means less need to modify the current technicalstandards.
However, the larger an earthquake, the larger theslippage in the hypocentral region. Also, if the area ofthe hypocentral region is large, duration of theearthquake is prolonged. So we have to watch forreciprocal response of ground motions accelerated byphenomena such as sympathetic vibrations.

5. Conclusion