A Pair of Large Earthquakes in the Indian Ocean

It's the stuff of nightmares at first glance, but there is some positive news about two huge earthquakes that struck several hundred miles offshore of Banda Aceh in Sumatra this morning. At 8:38 UTC (1:38 AM in the Pacific time zone) there was a magnitude 8.6 event with an estimated depth of about 14 miles. It was followed by a magnitude 8.2 event in the same region a little over two hours later. Given the horrific tragedy of 2004 when a tsunami generated in the region killed a quarter million people, this surely caused a sense of concern and panic. But there is a huge difference in the quakes that happened this morning.

The "beachball" symbols on the map above from the U.S. Geological Survey show the type of fault that produced the earthquake, and they indicate that this morning's quakes exhibited right-lateral strike-slip motion. This is good news because it means that the seafloor shifted sideways during the quake, instead of vertically. Accordingly, a large tsunami is unlikely, although a warning has been quite logically announced. Make no mistake, these are huge seismic events, and if they had occurred on land anywhere near a population center, they would have been horrible disasters. Preliminary news reports indicate that warning systems worked as people moved away from low ground along the coast. A sense of panic, no doubt, but at least there were warnings given, unlike in 2004.

For some details on the somewhat odd nature of these earthquakes, check out this analysis at Lithics.

8.9 Earthquake in Japan

We are learning more about a massive quake in Japan, with an estimated magnitude of 8.9 offshore of Sendai, Honshu. A major tsunami has been generated and the cable news shows are showing aerial shots of an extraordinary wave spreading across agricultural fields, overwhelming roads and villages. From the maps, it appears that the quake was generated in the subduction zone on the Pacific side. There is a good chance that a tsunami could be spreading through the Pacific, but I have not heard any confirmation. I would only say that if the authorities issue a warning, take it seriously and get to a safe place.

The most stunning aspect so far has been the aerial perspective of the tsunami spreading across the landscape. The 2004 tsunami in Indonesia was documented better than any previous event, but I don't recall seeing any aerial shots like this. Tsunamis are not really waves, they are surges of water that rush inland at speeds sometimes approaching 100 mph. The surge picks up debris and uses it as a battering ram. It is terrifying to see.

The TV commentators are starting to get up to speed, but for the best information from seismologists, check out the U.S. Geological Survey here. They have links to the current tsunami conditions in the Pacific basin.

My night class watched the 7.2 quake on Tuesday on our teaching seismograph, and I assume it was a foreshock to this event. Ironically, the subject of the day in my physical geology class was the types of damage caused by quakes. We mentioned tsunamis...

I pray for those in the path of the devastation.

UPDATE #1: A tsunami watch has been issued for the Hawaiian Islands. If a wave has been generated, it will arrive about 3 am Hawaii time.

UPDATE #2: The tsunami watch has been upgraded to a tsunami warning in Hawaii. Please take it seriously. The waves, if any, will reach the coast of California and Oregon around 7-7:30 am local time. At that distance, I don't expect much, but things can change overnight.

UPDATE #3: If 8.9 magnitude becomes official, this is the 5th largest quake in the world since 1900. Chile 1960, 9.5; Alaska 1964, 9.2; Sumatra 2004, 9.1; Kamchatka, Russia, 1952, 9.0. I finally hear an MSNBC commentator get the energy numbers right: the difference in energy between this and the Haiti quake at 7.0 is closer to 1,000 times, not 100 times. The equivalent of 1,000 Haiti quakes just hit offshore of Japan.

UPDATE #4: A tsunami watch has been announced for the coast of California. Take it seriously if you live in coastal areas. If it comes, it will arrive around 7:30-7:45 am in the morning. Listen for official warnings and obey them! Don't do the California thing and wander down to the beach to look for it.

UPDATE #5: The Pacific Coast is now under a tsunami warning, with expected wave heights of 3 feet or so, arriving around 8 in the morning depending on location. Take it seriously; if you are on the beach, you could easily be swept away by such waves. Follow official warnings; emergency personnel know what they are doing!

UPDATE #6: Some damage is now being reported in California as surges of water hit Crescent City and other coastal towns. Damage is "significant", not major, mostly along the lines of boats being jostled and ripped from moorings. I'm hearing of waves 5-6 feet high along parts of the California coast, and of 8 foot waves in Hawaii. 11 people were killed at Crescent City in 1964 from a tsunami of 12 feet, in part because they didn't realize the waves come in groups, and the first wave is not necessarily the largest. It is a cautionary tale for all the people rushing out to the beach to "see the tsunami". It might not be a good idea to become, literally, part of the story. Stay out of coastal areas until an "all clear" signal is given.

UPDATE #7: Silver Fox at Looking for Detachment has a list of the geoblogosphere's response to the Japan earthquake here.

UPDATE #8: Both the USGS and Japanese geologists have upgraded the magnitude of the quake to 9.0, making it the 4th largest ever recorded.

Words That Have Meaning: False Alarm and Warning (A Tsunami Wrap-up)

This was a false alarm? Photographs from CBS News and AP

Two situations:

In the first, it's a school day, and some kid pulls the fire alarm. Bells ring and students have to evacuate even though there is no evidence of a fire and everyone knows it was a prank. This is a false alarm.

In the second, a teller pushes the alarm button. There's a man demanding money. No one knows if the man is armed or not. The police evacuate the neighborhood, surround the bank, and ultimately arrest the man. If the man turns out to be unarmed, it makes the whole thing a false alarm, right? No? I don't think so either. The police and the people of the neighborhood were warned of a possible dangerous situation. There could have been a deadly shootout. Will anyone fault the police for doing their job?

So why are scientists being forced to defend themselves for their warnings about a tsunami? Just because the tsunami proved to have less violence than expected doesn't mean they should have acted any differently. The media bean-counters are probably sorry they didn't get the death and disaster in Hawaii and other Pacific Islands that would have driven up ratings (sorry for the cynicism), but the seismologists did nothing improper. And I was personally impressed that Hawaiians and others did such a fine job of responding. They know from experience what could have happened. And in the end, there was a tsunami that extended from Chile all the way to Japan where the pictures above were taken. There was a fine line between an interesting geologic event and a worldwide disaster. There is disaster enough in Chile, where the death toll continues to climb.

With that in mind, I'm glad to see the Pacific Tsunami Warning Center is not caving in to media accusations of a "false alarm":

"It's a key point to remember that we cannot under-warn. Failure to warn is not an option for us," said Dai Lin Wang, an oceanographer at the Pacific Tsunami Warning Center in Hawaii. "We cannot have a situation that we thought was no problem and then it's devastating. That just cannot happen."

The media should know better than to loosely toss the words "false alarm" in their wrap-up stories about the tsunami. Words have meaning, and "false alarm" sends the wrong message, a sort of "boy who cried wolf" attitude. Millions of people across the Pacific have now experienced an evacuation, and will know what to do the next time. Unless they think of the seismologists as boys crying wolf. These men and women take their jobs seriously, and will never play such games with the public.

Don't forget to donate to relief efforts in Chile, and in Haiti. It's so easy to forget a tragedy when another one crowds out the headlines.

UPDATE: Word starts creeping out about devastating tsunami damage in Chile

UPDATE #2: More people may have been killed in Chile by the tsunami than by the earthquake itself. Magma Cum Laude provides a nice example of good media coverage on the tsunami, with Dr. Chuck Bailey at William and Mary College. Nice catch!

UPDATE #3: Earth Magazine checks in with a good analysis of the quake and tsunami and links to some excellent media coverage by PBS News Hour (and thanks for the shout out for Geotripper, Magma Cum Laude, and Goodschist!)