Large Scale Urban Disasters and Telecommunications Networks

Dr. Keiji Tachikawa
Executive Vice President
Nippon Telegraph and Telephone Corporation

The Kobe Earthquake

A severely damaging vertical lifting earthquake occurred at 5:46 on the morning of January 17, 1995 in Kobe City near Osaka, Japan. Its epicentre was 20km below the surface with a great proportion of its impact heavily effecting the populated urban area. The magnitude was 7.2 on the Richter scale and the disaster killed approximately 5,500 people with more than 100,000 residences and buildings destroyed.

Japan happens to lie within a very geological active region of the earth, and regularly experiences a large number of earthquakes. Analysis of geological records reveals that large tremors resulting in loss of lives and damage to property occurs on average five times a year. Very large seismic events with a magnitude of 7 or greater occur approximately once every two or three years. Moreover, approximately 10 percent of all measurable earthquakes are centered under the region including Japan and its environs. The greater proportion of these are horizontal tremors occurring as the result of sliding at borders between plates under the sea surrounding Japan.

The Kobe earthquake was not one of those typical events, but rather involved a sharp vertical rise and fall at a fault line. Such events are thought to occur, on average, only every few thousand years. But when they do the damage is great.

Most of the telecommunications facilities affected by this disaster consisted of subscriber loop cable and wiring, subscriber loop switches and buildings. In the Kobe earthquake overall damage totaled approximately 30 billion yen. Destruction of telephone poles and buildings, as well as the numerous fires that followed the earthquake, caused failure to most aerial cables. Services to almost two hundred thousand subscribers were interrupted.

Damage to underground facilities such as cables in conduits was relatively minor, thus proving their overall reliability. Recovery for subscriber loop cables, however, was drastically delayed due to widespread destruction of residences and other buildings. Temporary facilities were used to get services back up within two weeks of the earthquake. Full service was restored eight weeks later.

Subscriber loop switches were themselves untouched. Such factors as long-term unavailability of public power supplies, as well as damage to backup batteries and emergency power generating equipment all combined to ensure that eleven switches in seven locations went down. Measures to bring them back up included bringing mobile power generating trucks to the area and all units were back functioning by the morning of the day after the earthquake.

NTT's building housing important telecom facilities have all been designed to seismic specifications. Damages to them were well within design parameters, and were not a factor directly affecting telecom system performance.

Telephone traffic after the earthquake, however, went far beyond anticipated levels, being 50 times as much as normal traffic on average. This was predominantly due to calls within and outside the area to confirm the safety of individuals, and resulted in most callers hearing a busy signal. In order to accommodate the necessary volume of emergency calls within the area as well as high-priority calls from outside the region, NTT conducted traffic control measures while also carrying out emergency expansion of circuit capacity. Nonetheless, we were not able to get traffic overflow under full control until one week after the earthquake.

NTT installed 3,000 new public telephones for the 300,000 residents of the area taking refuge in public accommodations, after suddenly finding themselves homeless. Satellite communications were an essential key to quickly getting this many new public phones up and functioning.

One major factor inhibiting the speed of recovery was the utter devastation to the public road and highway network. Numerous serious breaks in the road surface as well as other types of obstructions meant that trucks and other vehicles could not reliably transport cable-laying equipment. Every possible alternative such as helicopters (and under-sea cabling ships) were thus employed to get water, food, necessary materials, disaster workers and lines into the devastated area.

Disaster Countermeasures

Based on earlier experience with various types of disasters, NTT has been improving a lot of its counter measures against disasters, focusing on:

- enhancing system reliability,

- preventing communications service interruptions, and

- assuring quick service recovery.

A quick overview of major preventive measures looks like this:

• Enhancing System Reliability - Measures toward this focus have included: strengthening conduits, buildings and towers housing communications facilities; distributing long-distance switching equipment in such a way as to prevent breaks in trunk-call routing (separating them by more than 50km); and implementing automatic switchover systems providing multiple call relay routes including options away from disaster area.
• Preventing Communications Service Interruptions - Measures have included establishing radio facilities capable of supporting minimum essential communications capabilities in local government offices for each city, town and village.
• Assuring Quick Service Recovery - Measures toward this focus have included provision of: emergency-use portable telephone switches; power supply trucks; portable radio equipment; mobile satellite communications system earthstations; and emergency cable stock.

Conclusion

All measures have proven useful, and are in place nationwide. Another indispensable tool here has been regularly scheduled, periodic disaster training drills. Preventive measures in place before the disastrous Kobe earthquake were seen to work well when that quake hit. Design goals were met.

One phenomenon that was not well provided for, however, was the huge volume of telephone traffic that was experienced over the hours after news of the earthquake spread. Lack of capacity led to a very high rate of no-connects over a long period of time. Another improvement required is for the delivery of information to people who had to take refuge elsewhere after the destruction of their homes and property. Existing modes of communication were not up to the extraordinary demands of those first few hours and days.

To better prepare for the unfortunate events of such a large-scale disaster in the future, we are now laying plans for a stronger, more comprehensive response. Areas we are currently putting into active practice include: decreasing the required time for housing communications cable in underground conduits and pipelines; introducing more portable satellite communications systems; implementing robust voice mail systems capable of alleviating some of the worst aspects of traffic overloads at a time of crisis; and designing and constructing a disaster-region network capable of effectively delivering information to individuals and the public at large when their homes and places of work may have been badly damaged or destroyed.

One thing NTT certainly learned from this disaster was the importance of every-day planning and preparations for seemingly unlikely events - "Always be prepared".

Short Biography of Dr. Keiji Tachikawa

Dr. Keiji Tachikawa received his bachelor's degree from the Tokyo University in 1962, a MBA from MIT in 1978 and his doctorate in engineering from the Tokyo University in 1982. He has held many positions with Nippon Telegraph and Telephone Corporation (NTT) and is presently the Executive Vice President and Senior Executive Manager for Service Engineering Headquarters with NTT.

He is a senior member of IEEE and chief of the Tokyo region of Institute of Electronics, Information and Communications Engineers (IEICE) which is the largest communications-related technical institute in Japan.