Tsunami warning system?

Whatever happened to that Indian Ocean tsunami warning system, anyway?
Not enough, going off the devastation wreaked on the southern Javan coastline by another big wave.
With the death toll currently topping 530, and over 50,000 refugees, why is it the first warning most people got was the sound of rushing water?

Firstly, the facts of the quake (there has been some sloppy reporting of these):

When: 17th July, 08:24 UTC (15:24 local time).
How big: magnitude 7.7 (cw 9.3 for the boxing day 2004 tsunami).
How deep: Hypocentre was 48.6km below the seafloor (revised to 34km by USGS).
Where: the epicentre was 9.295° S 107.347° E, which is is 225km NE of Christmas Island, 240km SSW of Tasikmalaya, Indonesia, and 358 km S of Jakarta.

(data from US geological survey via Wikipedia).

Epicentre of the July 17th earthquake, surface fault boundary (red line) and local islands.


For the most part, people barely felt the original magntitude 7.7 quake. The first warning of the tsunami was when the first waves arrived over an hour later. Numerous aftershocks (54 and counting) have kept people on their toes since then.

And the press is starting to blame the scientists:

"SCIENTISTS can't stop them and they can't predict them. They can, however, send an alarm when a powerful tsunami is heading to shore. But for residents of southern Java there was no such warning on Monday when a near 3m high wall of water, triggered by a magnitude 7.7 earthquake 10km below the seabed, crashed on to a 300km stretch along scenic Pangandaran beach in Indonesia."

From The Australian. The lack of warning is not really a problem with the science - the detection systems are in place - even though in this region the plan's still in its infancy. None of the teams who detected in the earthquake could estimate the tsunami's size. Again from The Australian:

"It was the Hawaiian centre and Japan's Meteorological Agency that picked up Monday's quake and alerted the world. Both organisations issued warnings within 17 minutes of the quake, more than a half-hour before the tsunami hit Java's coastline.
In the open ocean a tsunami travels, on average, 800km/h. It slows when it reaches the shallower water of a coastline. "That's why the wave builds up," Jepsen says."

I've had difficulty finding the time difference between the quake, and the tsunami arriving at Java or Christmas island. Unconfirmed press reports indicate a period of 1 hour between the quake and the tsunami's arrival at the Javan coastline (240km), and 17 minutes to reach Christmas Island (225km). However, ABC news reports that Christmas Island had 20 minutes warning to get to higher ground. There seems to be discrepancy in the velocity - can changes in the wave speed explain it?

The speed of a tsunami is given by the equation vel=sqrt(g*d) ... where vel is the velocity (in m/s), g is gravity (9.81m/s^2) and d is the depth of the ocean at a given point (in m). If we assume the average depth of the seafloor is 5km between the epicentre and Christmas Island, then the velocity is 221m/s, or 795km/hr. Pretty fast. At this speed the tsunami would have crossed the 225km to Christmas Island in 17 minutes. Anywhere the depth is shallower would have slowed it down.

Chistmas Island only reported a 60cm swell - this is mostly because of the steep drop-off surrounding the Island - from land to 5ooom deep in a very short range. So the tsunami had no shallow shelf to slow down and build up height. When it approached Indonesia, on the other hand, the situation was different - it could build up to a 2-4m swell (depending on if you believe the tidal gauge or the people surfing it) before it hit. Not massive, but enough to inundate low-lying coastal villages.

So not much time to warn Christmas Island - but more time to warn Indonesia. What happened to the warnings? From Wikipedia (with news items referenced):

Indonesian government science and technology minister Kusmayanto Kadiman confirmed that Indonesian officials had received bulletins from both the Pacific Tsunami Warning Center in Hawaii and the Japan Meteorological Agency twenty minutes before the first tsunami wave struck but were too busy monitoring the quake aftershocks to issue warnings. ^[1]

According to an AP report, Science and Technology Minister Kusmayanto Kadiman stated that Indonesia received the warning bulletins 45 minutes before the tsunami hit. However, Kadiman indicated that the government did not publicize the bulletins because they did not want to cause unnecessary alarm. ^[2]

Edi Prihantoro, an official at Indonesia’s Ministry of Research and Technology that oversees a national warning project, said the southern Java area had no system to warn people of coming waves.

As part of a five-year project to install tsunami buoys around the archipelago, Indonesia deployed two such devices off the island of Sumatra last year. However, when asked how many of the deployed devices were operational, Prihantoro replied: “None.” He continued, “We need at least 22 buoys to cover all of Indonesia. We have received two from Germany and they were deployed months ago. However, both of them are damaged now.” Both devices have since been decommissioned and one of them is awaiting repairs. ^[3]

References

1. ^ "Officials failed to pass on tsunami warning", Guardian Unlimited, 2006-07-18. Retrieved on 2006-07-18.
2. ^ "Java death toll tops 500", CNN, 2006-07-19. Retrieved on 2006-07-19.
3. ^ "Indonesia's 2 tsunami alert buoys were busted", MS/NBC, 2006-07-18. Retrieved on 2006-07-18.

So the warnings were issued but the Indonesian government failed to pass them on. Plus the buoys the were given were trashed and not fixed/replaced. Now we are at the crux of the problem. An early warning system will only be effective if local authorities act on the warnings, and take the system seriously. The tragedy of 500+ people's deaths, while probably not completely unavoidable, could have been mitigated if the Indonesian authorities had acted on the early warnings they were given.