Happy Holidays all--and Enjoy "Santa Never Made it to Darwin" once again!

Hi, folks,

I hope that the holidays are happy for all, and send best wishes for 2012!

The Bill and Boyd song that you can find in the post below reminds us that natural earth processes don't actually know about holidays.

http://www.geologyinmotion.com/2011/01/cyclone-tracy-and-santa-never-made-it.html

Power and energy of the Tohoku tsunami: Revised estimates.

Last March 12, a day after the Tohoku earthquake and tsunami, I posted an estimate of the power and energy in the tsunami, based on a rough estimate from observations at the time. My conclusion was that the energy was about 30 kilotons, roughly equivalent to the energy in the combined bombs that were dropped on Hiroshima and Nagasaki (36 kt). I felt that the energy could have been a factor of ten or a hundred higher given uncertainties in the height of the waves and duration of the event. Thanks to a reader's inquiry, here are some updated numbers based on data that has since emerged.

(Please give credit to this blog site if you use the numbers posted below!)

First, let me summarize the method.  Professor Michael McIntyre of the University of Cambridge calculated the power in a tsunami using Bernoulli's theorem, and concluded that under certain conditions the power in a tsunami is about 1 megawatt per meter of shoreline, or 1 gigawatt per kilometer.  The conditions are that the tsunami has a height of 1 meter in the open ocean, a velocity of 220 meters per second. I used these data directly and assumed a similar power, then estimated the length of shoreline attacked (one-half of the east coast of Honshu) and the duration of the tsunami (100-1000 seconds).  The model applies to tsunamis on the open ocean.

There are still not a lot of data available, but the velocity of 220 meters a second for the speed of the tsunami is in the right ballpark to account for the time between the earthquake and the time that it took for the tsunami to reach the coast (30-60 minutes).  The major uncertainty here is the height of the tsunami on the open ocean. I used the value of 1 meter that is typically used for tsunamis (because they are typically not even noticed on the open ocean). There were two ocean-bottom sensors in place that measured a height of 7 meters (Maeda, Takuto et al., Earth Planets Space, 63, 2011, in press) where the water was 1618 m and 1013 m deep respectively, and so I'll use a new value of 7 meters for the open-ocean height of the tsunami.

McIntyre's calculation of the power in the tsunami was based on an ocean depth of about 4.5 kilometers--deep open ocean.  In order to make my calculation internally consistent, I need to use shallower depth of, say 1.5 kilometers.The power, as calculated by McIntyre, is proportional to the depth to the three-halves power.

The height of the tsunami comes into the calculation as h-squared; the depth of the ocean as a square root.  Thus, the smaller ocean depth would reduce the power by a factor of 1.7 (sqrt 4.5/2) and the greater height of the tsunami would increase it by a factor of 49 (7 squared). The combined effects cause an increase of 28.8 in the power (let's round it up to 30).

To get energy from this, I assumed that the event lasted 100-1000 seconds, and that the length of coastline affected was about 1300 km. Both assumptions still seem reasonable. If you look at the map above of wave heights impacting Honshu, the northern half of the island, which is the half that I originally assumed was affected, has significantly greater wave heights than the southern half. Furthermore, for the model to be internally consistent, the number I really need is the length of the tsunami out on the open ocean not the amount of shoreline impacted. However, the assumption that the length of the tsunami was about equal to the length of the northern half of the island should give a ballpark estimate of the length at sea.

To summarize: I would increase my original estimate of the minimum power from  1.3*10^12 watts or 1.3 petawatts to 40 petawatts, and my original estimate of minimum energy to 40*10^14 joules or 930 kiloton, which could easily be rounded up to 1 megaton. These are the power and energy for an event of 100 seconds duration.  I believe that a more realistic duration is 1000 seconds, giving 400 petawatts and 10 megatons as the preferred values.  Note: Please See the first comment by a reader. Suggests that something between the min and max would be a better number to use.  So, perhaps best to say "a few hundred petawatts" and "a few megatons" given all of the uncertainties. 

 (For comparison, the 400 Pw and 10 Mt values are about 280 times the the combined energy of the bombs that destroyed Hiroshima and Nagasaki (15+21 kilotons.) The energy of the lateral blast at Mount St. Helens was about 24 megatons.)

Please see reader comments!

Tohoku tsunami IN THE PACIFIC was a "merged tsunami" (Or was it? Why did I put IN THE PACIFIC in capital letters? Read on!)

Left: Ocean heights as observed by two satellites.
Top: at 7:30 hours; Bottom, at 8:20 hours
Right: Computer simulations (black lines) and data
(red and purple lines) on the form of the tsunami.
NASA/JPL-Caltech/Ohio State University
The NASA press release is here.

The Fall meeting of the American Geophysical Union is in full swing and press releases are highlighting some interesting papers. One of these is on so-called "merged tsunamis," which I'll explain in a minute. However, if you Google "merged tsunamis" today, you'll find headlines like:

"Two merging tsunamis caused Japanese devastation" (TG Daily)

"Double Tsunami" Doubled Japan Destruction" (Eurasia Review)

"Rare "merging tsunami" contributed to Japan destruction" (Mother Nature Network)

Even mainstream newspapers:

"Japan was hit by a tsunami formed from TWO giant waves, reveal scientists" (Daily Mail, UK) (OOOPs, note added: one commenter pointed out that the Daily Mail should not be considered a mainstream newspaper...)

"Tsunami that struck Japan in March resulted from merging waves" (CNN, International)

Even academic publications:

"Merging tsunami" doubled destructive power along Japanese coast" (Environment360, from Yale.edu)

Many of the articles are accompanied by photos of the devastation on the coast of Japan.

But, wait a minute!! Here's the actual NASA/JPL news release. While the headline "NASA finds Japan tsunami waves merged, doubling power," might lead you to think that scientists are saying "The tsunami that hit Japan was caused by merged tsunami waves, doubling the power...", that is, in fact, not what the text of the article, nor the accompanying images show.  If you look at the images shown on this post (which are the images in the press release) carefully, Japan is in the far upper left corner and the waves that were observed and are modeled are far out away from Japan in the Pacific Ocean. They were observed 7:30 and 8:20 hours AFTER the earthquake.  In contrast, the waves that devastated northern Honshu struck in 20 minutes.

Unfortunately, I am not at AGU to hear the paper (which is not being given until Friday morning), but I find the press release to have very little content--it basically says that two satellites captured the above two images, that there was a "merged tsunami," and that this merging phenomenon may account for unexpected destructive power." And, I find the images to be baffling....what do the three black arrows point to? What is the purple line that runs up through the bottom image, and why is it red in the top image? What is the red arrow on the bottom of each image and why has it changed position? What am I supposed to be seeing in these images?  The abstract of the actual paper (by Y. Tony Song and others) has a different figure). For info, I have attached the actual abstract at the bottom of this post.

Here's what I do see--in both images the red areas show water that is higher than an arbitrary zero-level (see the scale on the left image). The blue areas, in contrast, represent water that is below the zero level.  These two areas correspond to the highest and lowest peaks in the model and data shown on the right side of the figure. All that I can pull out of the two images on the left side is that there isn't as much red or as much blue in the bottom image as in the top one--that is, the high water is less high, and the low water is less deep, which is what you expect as a tsunami spreads out to cover more and more area. My concept of a "merged tsunami" is that two high waves catch up with each other producing a bigger wave by constructive interference.  I can't see that in these images.

Readers--HELP!! (And they did, see reader comments!)

And, JPL--shame on you for an ambiguous, if not downright misleading, headline. It did its job in attracting a lot of attention, but it created a lot of misinformation, and that's not the job of a scientific press release.

______________________________________________________________________________________

ABSTRACT FINAL ID: NH51C-02;

TITLE: Merging Tsunamis of the 2011 Tohoku-Oki Earthquake Observed from Space (Invited)

SESSION TYPE: Oral

SESSION TITLE: NH51C. Remote Sensing of Natural Hazards I

AUTHORS (FIRST NAME, LAST NAME): Y Tony Song1, Ichiro Fukumori1, Yuchan Yi2, C. K. Shum2

INSTITUTIONS (ALL): 1. CALTECH/MS 300-323, Jet Propulsion Laboratory, Pasadena, CA, United States. 2. Ohio State University, Columbia, OH, United States.

Title of Team:

ABSTRACT BODY: Tsunamis often severely devastate some coastal areas while leaving others with little damage. This unpredictable situation has been a major challenge for accurate and timely tsunami forecasting for evacuating coastal communities. Here we show evidence from satellite observations of the 2011 Tohoku-Oki earthquake-induced tsunami that sheds light on this issue. Three satellites observed the same tsunami front, and for the first time, one of them recorded a tsunami height about twice as high as that of the other two. Model simulations confirm that the amplified tsunami is one of several jets formed through topographic refraction when tsunamis travel across ocean ridges and seamount chains. This process causes the tsunami front to merge as it propagates, resulting in doubling its wave height and destructive potential in certain directions before reaching shore. We conclude that the potential of tsunami merging jets should be taken into consideration for designing coastal tsunami hazard maps and assessing risk levels at coastal oil refineries and nuclear power facilities. http://science.jpl.nasa.gov/people/Song/

KEYWORDS: [0933] EXPLORATION GEOPHYSICS / Remote sensing, [4564] OCEANOGRAPHY: PHYSICAL / Tsunamis and storm surges, [7215] SEISMOLOGY / Earthquake source observations.

(No Table Selected)

SPONSOR NAME: Y Tony Song

Additional Details

Previously Presented Material:

Contact Details

CONTACT (NAME ONLY): Y Tony Song

CONTACT (E-MAIL ONLY): yuhe.t.song@jpl.nasa.gov

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Santa Ana winds pummel southern California; Pasadena declares state of emergency

Tree attacks gas station in Pasadena, California
This does bring back memories--I lived only a few blocks from
here when I was a grad student at Caltech!
Photo by KTLA published in the Los Angeles Times

Updated: 9:20 a.m. CST Thursday 12/01.
Updated: 7:15 p.m. CST, Thursday 12/01.

Wind gusts up to 97 miles per hour are pummeling southern California, causing fires, downing electrical wires, and toppling trees. (Update: Winds up to 140 miles per hour have been recorded at the crest of the Sierras). According to the LATimes, firefighters were being dispatched every 12 seconds in response to emergency calls on downed electrical lines. As of this morning, over 25,000 people are without power, and the winds are expected to continue through Thursday. LA airport was having problems with debris on the runways, but flights are being allowed to land. Update: Pasadena has reported up to 200,000 people without power, and has closed schools and libraries until further notice.

Raymond Chandler described these winds in his 1938 novel, "Red Wind": 

"There was a desert wind blowing that night. It was one of those hot dry Santa Anas that come down through the mountain passes and curl your hair and makes your nerves jump and your skin itch. On nights like that every booze party ends in a fight. Meek little wives feel the edge of the carving knife and study their husbands' necks. Anything can happen. You can get a full glass of beer at a cocktail lounge."

Santa Ana winds are one type of wind called "katabatic" winds. Katabatic is derived from the Greek word "katabatikos" meaning "going downhill." They occur in numerous places around the world.  In southern California they form when air flows from the Great Basin of Nevada westward to the Pacific Coast. As the air flows downhill, it compresses and becomes denser. This compression causes the air to warm and in the summer the winds feel like a blast from a furnace. In the winter, however, this process isn't strong enough to overcome the fact that the air is very cold when it starts from the Great Basin and the winds can bring some of the coldest weather of the season into LA.  The temperatures were down in the forties last night.

Although there was only one fire yesterday and it was quickly controlled, Santa Anas in the autumn can be extremely dangerous--the humidity is low, abundant summer vegetation dries out, and the winds can fan huge fires if they get out of control. The LA fire department has boosted its staffing and declared a "red flag warning" of high fire danger. The Santa Anas are also dangerous to peoples health because they can carry a pathogenic fungus spore that causes Valley Fever (Coccidioidomycosis), an influenza like condition.

Update: More meteorology: There is a counter-clockwise low-pressure system parked over California, and a clockwise high-pressure system over Arizona, Nevada, and the Great Basin. These two systems are funneling the winds into California.  Here's an AccuWeather update. The winds are expected to continue into Friday. Pasadena seems to be the "epicenter" of the storms.