On Kobe earthquake

Japan being an affluent state with state of art knowledge on seismology and especially being aware of the risk factors of earthquake as a hazard,must have taken very good care in the construction of buildings-residential or otherwise in the mitigation of effects from earthquakes.under the circumstance Iam unable to understand the very heavy building collapse associated with kobe earthquake.what is the real cause behind this failure of structures?

Many buildings in the affected areas had been built in accordance with the older construction law (requiring lesser degree of earthquake-resistance). And the quake was of a such magnitude and intensity that even raised freeway structures were destroyed.

Also, resulting fire that broke out (in areas where detached houses were built closely together) added to the casualty.

Please note that science to predict earthquakes has yet to be established, and that architecture that withstands "any" earthquake would probably be unusable as buildings.

...let alone extremely costly and prohibitive.

I've seen some Japanese shows where devices that actually lift the house on giant rubber blisters have been used to reduce the intensity of seismic activity. But these are new and relatively untested and built for one or two story homes.

Without minimizing what happened,the news on many TV channels and on numerous videos were showing the few same areas again and again.

At the same time, other areas nearby hardly had any damage. Friends of mine owned an old wood house they had planned to tear down for years..It was not damaged by the quake at all (they slept through it) but when some much newer houses next door--in concrete-- that were badly damaged started to burn (the water heater pilot light igniting leaking gas), so did their old house...

Some newer medium height apartment buildings felt sideways, nearly unbroken but useless! An apartment building near my friends house had glass railings on all the balconies. They didn't break, the building was fine.

I met a guy who owned a plain cheap brick building from the 1930s that was not damaged at all.

It looks like that what matter the most is why the ground shift and breaks..buildings there will collapse, while others on a more stable ground, will not.
However in another quake the ground will be weak in areas different front those of the previous quake..It is all random and perfect buildings haven't been invented yet.

I was in Kobe not long before the quake and have gone back many time since and can tell by looking at buildings---I used to build houses and small apartment buildings--which ones were old in 95 and weren't damaged or only slightly. They are quite numerous.

I was there when that hit, we used to live in a 5-storied concrete apartment building with a basement garage (the pillars were quite big, it was apparently built to the new standard, no compromise), and ours survived. We were awoken violently by the quake, and when we went outside, to our horror, a few of other concrete buildings with shops on the ground floor - meaning more glass windows, less wall, thinner pillars - had been badly damaged. One (several-storied) was slanted, and another (probably had about ten floors or so) had come down one floor, with the ground-level floor completed crushed to the ground. Many other old-style wooden residential houses had collapsed too. That was in Hidashi-nada-ku, where it was pretty bad... later we went to check on my husband's colleague's house, a bit closer to the ocean, and her apartment building was intact. I guess our area had a solid rock, meaning the shift directly got transmitted, tearing the ground on which the buildings stood. It really depends on the exact location/soil/rock beneath.

Just to add, the Kobe quake was an unexpectedly verticle shake that make heavy plant pots literally jump over high walls. That was something construction law-makers were never used to. People were mainly thinking about horizontal shakes until then.

Also, just as it is with most countries around the world, we have come to know that many buildings have cracks and leaks that aren't taken care of properly, and that has led to accidents here and there even apart from the Kobe quake.

Plus, the big reason for fires in Kobe was that, in certain areas, many of the streets were just too narrow for fire engines to come into, and due to the many fires, fire hydrants were running out of water. In other words, in usual circumstances, fire engines would get water from far away hydrants even if they couldn't go into the narrow streets, but that wasn't possible in the Great Kobe quake. So nowadays, whenever a building is torn down, they make sure the streets are spread wide enough for a fire engine to come through.

These are probably the main elements as far as construction is concerned.

Uco makes a valid point..unfortunately underground water pipes can and do break if the ground moves a lot, then fire hydrants get no water!