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'@-L-Iwfw, or- mbo Irk MI THE GREAT WAVA@-' GC 222 T3 U55 1975 W% DEPARTMENT OF COMMERCE XTUMT1 Oceanic and =-t - Weather Service 00 d) :IFIC ---------- ------------------------ - ----------------- t A C -71 0 0 Nk J 15 ---------- ---------- ------- ------ .jw, -7@ Y IS COVERED LIKE AN ARMORED REPTILE with enormous stony slabs which drift on the denser material of the mantle, slabs which are constantly being destroyed and renewed in the processes of "plate tectonics." As they drift they push continents together and tear .7 @1 @,DG them apart over long stretches of geologic J time, and cause the massive accumulations and sudden releases of energy we experience in the form of major earthquakes. Nowhere are these processes more in evi- dence than along the belt of frequent earth- . .... .. ...... ... . .. . .. ....... quakes and volcanic eruptions that rings the Pacific Ocean. This circum-Pacific belt is the earth's most active seismic feature, a place World seismicity map by the where myth-sized earthquakes still shake NATIONAL EARTHQUAKE INFORMATION SERVICE, down the fragile things men build. 2 ---------- ---------- % arthquakes, the destructive off - And these e spring of larger forces shaping and reshaping planet earth, have destructive oceanic off - spring of their own-the great waves of the Pacific. Every island and coastal settlement in the Pacific Ocean area is vulnerable to the on- slaught of the great waves. Those of 1868 and 1877 devastated towns in northern Chile, and caused death and damage across the Pacific. A series of waves generated by the eruption and collapse of Krakatoa in 1883 killed more than 36,000 persons in the East Indies. Japan lost 27,000 lives to the wave of 1896, and 1,000 more to that of 1933. There have been hundreds more whose effects were less spec- tacular but which took many lives and did much damage. The 1946 waves which struck Hawa'" are a case in point. And the waves sent out"by the 1960 Chilean earthquakes. And the Great Alaskan earthquake's sea waves, which 1964 cau"sed damage as far away as Cali- fornia, Hawaii, Chile, and Japan. Some call them "tidal waves," a name as misleading as it has been persistent. The great waves are not related to the tides. The Japanese, whose islands have felt their de- structive power for generations, give us the name used internationally: tsunami.* pronounced "soo-nah'-me" (IN rV ilt NNIS, top CN ,Adw@ phenomenon we call "tsunami" is a tion-rep resented by a tsunami is impressive: z4fta;@ of traveling ocean waves of extremely a tsunami "feels the bottom" even in the length and period. In the deep ocean, deepest ocean, and it appears that the pro- 419T, length from crest to crest may be a gress of this imperceptible series of waves 7 WITT-o miles or more, their height from represents the movement of the entire verti- rjW9 t to crest only a few feet. They cannot cal section of ocean through which the ei:@ felt aboard ships in deep water, and they tsunami passes. In the deep ocean, the waves WH MM be seen from the air. may reach speeds of 600 miles per hour. M: the kinetic energy-the energy of mo- As the tsunami enters the shoaling water -raft, 99RNW 4P AW A# 4k@ z tsunami wave sequence shows (1) water draining away from the beach as the tsunami trough approaches followed by (2) the churning onslaught of the wave crest, and (3) the great wave all the way in. These photo- were taken by Rev. S. N. McCain, Jr., Kauai, Hawa ii. of coastlines in its path, the velocity of its magnitude and depth, water depth in the re- waves diminishes and wave height increases. gion of tsunami generation, the amount of The arrival of a tsunami is often (but not al- vertical motion of the sea floor, the velocity ways) heralded by a gradual recession of of such motion, and the efficiency with which coastal water, when the trough precedes the energy is transferred from the earth's crust first crest; or by a rise in water level of about to ocean water are all part of the tsunami one-half the amplitude of the subsequent re- birth equation. cession. This is nature's warning that more And there are other difficult questions. Ex- severe tsunami waves are approaching. It is cept for focusing effects on tsunami wave a warning to be heeded, for tsunami waves energy, particularly the well-studied tsunamis can crest to heights of more than 100 feet, of 1960 and 1964, not much is known about and strike with devastating force. the relationship between ocean floor config- Tsunamis are caused by large earthquakes uration and the shape taken by tsunamis centered under or near the ocean-specifi- there. It is not completely clear, for example, cally, by the net vertical displacement of the why a tsunami's waves may be of negligible ocean floor caused by such disturbances. size at one point along a coast, and much These displacements can also be produced larger at other coastal points nearby. Tsunami by volcanic eruptions and the submarine ava- run-up-the vertical distance between the lanches along the slopes of Pacific trenches, maximum height reached by the water on events which have been linked to tsunami shore and the mean-sea-level surface-is generation. also impossible to predict at the present time. But the tsunami-generating process is more Nor is it possible to predict whether the de- complicated than a sudden push against the structive component of a tsunami will lie in column of ocean water. The earthquake's its powerful surge across a beach, or in a gradual rising of sea level followed by a rapid draining back to sea. The key known characteristic of tsunamis is that their speed varies with the square root of water depth. It is this relationship which permits prediction of tsunami arrival times at all points in the Pacific Ocean area. Speed (mph) 670 600 519 424 Depth (feet) 30,000 24,000 18,000 12,000 Vertical displacement. Submarine Avalanches. 299 94 30 --6,000 3,000 600 60 Tsunami speed is determined solely by water depth, and this fixed relationship makes it possible to forecast tsunami arrival times for distant locations. The tsunami illustrated here, although somewhat exaggerated in the vertical dimension, is characteristic. Warnpr IF,* 'now 0sm, In the early morning of April 1, 1946, a vio- Scotch Cap lighthouse before ... lent earthquake disturbed the northern slope of the Aleutian Trench, and triggered one of the most destructive tsunamis in recent years. Minutes after the earthquake occurred, waves more than 100 feet high smashed the light- V house at Scotch Cap, Unimak Island, killin 9 pa- five. The first wave struck Hawaii less than five hours later. When the tsunami had gone, 159 persons were dead and 163 injured, and the islands had suffered some $25 million in property damage-the worst natural disaster ko in Hawaiian history. 7- -sixth tsunami recorded This was the thirty Ad in Hawaii in 127 years, and the first to do severe damage since 1877; other major tsu- namis struck the islands in 1837, and twice ... and after the April 1946 Alaska tsunami. in 1868. They came without warning, as the great waves had always come in the Pacific. But the tsunami of April 1946 would be the last destructive tsunami to surprise Hawaii. To a group of scientists in what is now the National Oceanic and Atmospheric Adminis- jtf tration of the U.S. Department of Commerce, Nil there was nothing inevitable about the 1946 01, disaster in Hawaii. The victims of the tsunami, they believed, could have been warned and saved. And tsunamis could be detected and their arrival predicted with sufficient accuracy to provide early warning to the people of Hawaii. A_ - The tsunami warning system they envi- sioned would use seismographs to detect and 8 ng ste The 1946 tsunami roars into Hilo harbor ... locate earthquakes, and tide gages to detect passing tsunami waves. These would be linked by an extensive communications net- Atop., - work. It took two years and considerable tail- *i, oring of existing instruments and techniques to transform the belief into a functioning reality. In 1948, what was then called the Seismic S -Wave Warning System was put into op- ea eration with its headquarters at the former Coast and Geodetic Survey's magnetic and %--now seismological observatory near Honolulu. During the next four years, the system de tected many submarine earthquakes, but no major tsunamis developed, and no full-scale alerts were necessary. Then, on November 4, ... causing widespread destruction in the Hawaiian city. 1952, a submarine earthquake near the Kam- chatka Peninsula generated a tsunami felt across the Pacific. The waves caused some $800,000 damage in Hawaii, but they took no lives. The warning system had begun to pay its way. Until 1964, three major tsunamis had crossed the Pacific since the Kamchatka tsu- nami of 1952. The Aleutian tsunami of March 9, 1957, caused damage in the Aleutians, Hawaii, Japan, and along the west coast of North America, but no lives were lost. The Chilean tsunami of May 1960 was the most destructive in recent history, causing deaths and extensive damage in Chile, Ha- waii, the Philippines, Okinawa, and Japan. Waves 15 to 35 feet high pounded the Hawaii 9 city of Hilo, leaving 61 dead and causing $22 On March 28, 1964, a magnitude 8.5 earth- million property damage. But a warning had quake struck the Prince William Sound area preceded the waves in Hawaii by six hours; of Alaska. Called the Good Friday earth- the toll might have been much worse. quake, this largest North American tremor In Japan, no general tsunami alert was is- ever recorded generated a tsunami that was sued for it was not known then that a tsunami felt across the ocean. Considerable damage of such distant origin could be so destructive. was done along the coasts of Alaska and The waves left at least 180 persons dead or Canada, and at Crescent City, California. And missing in northern Japan and Okinawa, 20 there were casualties. But the number was in dead in the Philippines, caused $500,000 tens, not hundreds and not thousands. Warn- damage along the western coast of the United ings make an important difference! States, and did considerable damage in New Today's Tsunami Warning System, oper- Zealand. All Chilean coastal towns between ated by NOAA's National Weather Service, is the 36th and 44th parallels were destroyed or a truly international service, providing timely severely damaged. warning to 14 Pacific coastal and island na- The third large tsunami, which originated tions and territories, including the United off the coast of Peru on November 20, 1960, States. Honolulu Observatory is headquarters caused 11 deaths on nearby coasts but did for the Tsunami Warning System, and the little damage in other Pacific areas. nerve center of an ocean-wide network of detectors. Here, the 24-hour watch is kept for the first reactions of instruments thousands of miles away. ELAPSED TIME- SOURCE EPICENTER EARTHQUAKE PLUS: 3 minutes 35 seconds 6 minutes 9 seconds 8 minutes 19 seconds 10 minutes 9 seconds All 11 minutes 42 seconds Y, Kz P INNER COA E M 'Al S-Mves P-Waves 10 Most earthquakes are caused by slippage In addition, a network of seismograph sta- along strained faults in the earth's crust. The tions around the Pacific contributes data as sudden release of energy as these faults it comes in and is analyzed. Some of these move toward equilibrium produces a variety are operated domestically by other govern- of earthquake waves, which travel through ment agencies and private institutions, and the earth and across its surface. At seismo- some are the private and governmental seis- graph stations, these waves are picked up mological observatories of cooperating Pa- and translated into electrical signals, which cific nations. When an earthquake of suf- are further translated into a written record ficient magnitude to generate a tsunami that becomes the earthquake's "signature." occurs, each seismograph station equipped From this signature, or seismogram, seismol- with an automatic alarm comes to alert, and ogists can determine the approximate magni- the watch and warning process begins. tude of the earthquake, and the surface dis- As the computers and scientists at Hono- tance between their seismograph station and lulu Observatory go to work on the develop- the source of the disturbance. ing tsunarhi emergency, participating seis- A diamond-shaped "quad ri partite" array mograph stations begin reporting the local of seismic detectors on the island of Oahu, arrival times of earthquake waves. Because linked to Honolulu Observatory, forms the first the propagative characteristics of earthquake line of detection for the Tsunami Warning waves are well established, the time interval System. The array permits automatic calcu- between P (compressional, push-pull) and S lations of the surface point of origin (the epi- (up-and-down and side-to-side shaking) center) of incoming earthquake waves, earth- waves can be used to compute the surface quake magnitude, and something about the distance between each seismograph station tsunami-generating potential of the earth- and the source of the disturbance. The inter- quake. (Earthquakes below magnitude 6.5, for example, are not considered tsunami- genic, nor are earthquakes occurring in areas characterized by horizontal fault motion.) The difference between P and S wave arrival time at each seismograph station can be used to calculate the distance between the source and the seismograph locations. If the source falls near or under the ocean, and the earthquake is large enough, a tsunami watch goes out across the Pacific. P wave S wave min. section of these arcs of surface distance-in a computer program or on a world globe- s is the earthquake epicenter. If this point falls on or near the ocean, tsunami generation is possible. On the basis of such seismographic evi- dence, Honolulu Observatory issues a tsu- nami watch, which tells Tsunami Warning System participants that an earthquake has occurred, and where, and that the possibility of tsunami generation exists. Estimated times of arrival are also computed and transmitted for each participant's location. Now the warning system turns to its sec- ond line of detection: a Pacific-wide network of tide stations. There, gages continuously record the cycles of the tides. Passing tsu- namis appear on the tidal record, or mark gram, as distinctive abnormalities. With the occurrence of a major earthquake, Tsunami Warning System headquarters requests tide observers closest to the epicenter to check their record for "unusual activity." The first positive indication that a tsunami I@ET exists usually comes from tide stations near- est the disturbance. When confirmation is re- ceived, Honolulu Observatory issues its warn- ing, alerting warning system participants to the approach of a potentially destructive ser- ies of waves and repeating tsunami estimated arrival-times for each location. Local warning, evacuation, and other emer- Tsunami waves gency procedures are then undertaken by designated emergency and relief forces in 2-m the regions covered by the warning. Because the main benefit of the Tsunami Warning Sys- 9 `We tem is to give participants time to prepare for the waves, transmission of watches and warn- ings is limited to a single point in each coun- try, territory, or state. Normal waves These warning points differ from region to region. In the United States, Canada, and New Zealand, the messages are usually di- rected via military and aviation communica- tions links to regional civil defense and other natural disaster offices. In Chile, the Depart- FEL ment of Navigation and Hydrography is the tsunami warning agency. In Japan, the Philip- pines, and Taiwan, the national meteorologi- cal agency disseminates tsunami warnings to local and regional civil defense organizations. In the Fiji Islands it is the Harbour Master. Tsunamis appear on the tide gage records, or marl- In Pap ua and New Guinea, tsunami warnings grams, as distinct abnormalities. Marigrams are usually come in over aviation lines and are dissemi- the first positive evidence that an earthquake has gen- nated to the general public by the Civil De- erated a tsunami. With the existence of a wave con- fense and Emergency Services organization. firmed, the tsunami watch becomes a tsunami warning. In Nauru such dissemination is the respon- 12 sibility of the Chief Secretary of the Republic; in French Polynesia and New Caledonia, the warning office is designated by the Governor. In Hong Kong, warnings are relayed by the Royal Observatory to the Government Information Services Department, which disseminates them to the general public. In Tahiti, warnings are received and disseminated by the geophysical laboratory there. Because tsunamis respect no national boundaries and because close lisison is essential between participating nations in the Tsunami Warning System, an International Coordination Group has been established, composed of intereted member nations in the Intergovernmental Oceangraphic Commission. The group helps tie togethr the three distinct tsunami warnings operations in the Pacific-those of the United States, the Soviet Union, and Japan-and generally promotes liaison and information exchange in the areas of tsunami detection and forecasting. It also deals with the establishement and operation of the International Tsunami Information Center at the Pacific Regional Headquarters of NOAA's National Weather Service and with World Data Center A for Tsunamis, located at the National Geophysical and Solar-Terrestrial Data Center (of NOAA's Environmental Data Service) in Boulder, Colorado. Nations participating in the International Coordination Group include Canada, Chile, Ecuador, France, Guatemala, Japan, Korea, New Zealand, Peru, the Philippines, Taiwan, Thailand, the United States, and the Soviet Union. 13 El 40@491064#H WArn'N"@] Systems One of the important lessons of the 1964 sis operations at Palmer are only part of the Alaska earthquake was that a tsunami can regional system. The rest is communications swamp a coastal area near its epicenter long -direct lines to crucial coastal communities, before Honolulu Observatory can confirm that seismograph observatories, civil defense a tsunami has been generated. The result of units, and other emergency forces-which that lesson has been the establishment of two help speed the urgent tsunami word to those fast-response regional tsunami warning sys- who must put the warning to work. tems, one for Alaska and one for the Hawaiian When a major earthquake of magnitude 7 islands. or greater occurs along the Pacific coast of The regional system in Alaska, operational Alaska, an immediate tsunami warning is is- since 1967, represents a unique collection of sued for an area for at least a 200-mile radius the most sophisticated equipment and tech- around the epicenter, and including a Palmer niques available to seismologists today. The system tide gage on two sides of the epi- system's nerve center is Palmer Observatory, center. An immediate tsunami watch is issued north of Anchorage, a highly automated head- for the rest of the Alaskan coastline. If sig- quarters linked to telemetering robot tide and nificant tsunami wave activity is detected on seismograph stations from Sitka to Shemya. the marigrams (tide-gage records) teleme- The sophisticated data-collection and analy- tered into Palmer, the warning is extended &INDIAN MOUNTAIN GRANITE OUNTAINA &GILMORE CREEK ABLACK RAPIDS ATOLSONA PALMER WEST PALMER OBSERVATORY I PALMER SOUTH\2@@ S WARD YAKUTAT A MIDDLETON ISLAND SITKA OBSERVATORY KODIAK -ISHEMYA D POINT REPORTING STATIONS ADAK NE 4.DAK OBSERVATORY TIDE STATIONS 1_0UNALASKA SEISMOGRAPH STATIONS -to, . , . -, @p I-ALTERNATE NAME @@HOUSTON ADAK SE NIKOLSKI 2-ALTERNATE NAME ARCTIC VALLEY" PALM @.INDIA. MOUNTAIN I A WE AL@ PA, S 2@ARD I KO DIAK D PO' NT 14 Opona Koeno Pt. OAHU Honolulu Observatory Mokopo Honolulu MOLOKAI Haleakala MAUI Mouno Kea Kona b Hawaiian Volcano I Observatory I Pahoo HAWAII Honuopo REPORTING STATIONS * Radio Telemetry Network * Tide Stations A Seismograph Stations to include Alaska's entire coastline. Severe coastal earthquakes cause Palmer to issue an immediate tsunami warning for at least a 500 mile radius around the epicenter. The Hawaii regional system entered service in 1975 to provide similar protection against locally generated tsunamis for the people of Hawaii. Directed from Honolulu Observatory, the Hawaiian system receives telemetered data from a quadripartite seismograph sys- tem on Oahu and stations on the big island of Hawaii and Maui. These, and telemetering tide stations and offshore pressure-sensing (tsunami-detecting) instruments on the ocean Z floor, provide continuous seismic and water level data. When an earthquake occurs in the Hawai- ian region of a size and location that make tsunami generation possible, Honolulu Ob- servatory issues warning messages to the threatened coastal areas through Hawaii Civil Defense. Meanwhile, observatory personnel monitor incoming tide gage data to determine whether a tsunami has been generated. If none has, the warning is quickly canceled. The rule of thumb in both the regional systems is to get the warning out within min- utes of an earthquake and to keep informa- tion flowing to emergency forces and the public until the danger is past. Tsunami alarm sirens. 16 The difference will be that the spacecraft in NOAA's operational series will be able to Into the pass on the questions and answers between a computer at Honolulu Observatory and automated seismic and tide stations around Amrl@ the Pacific. This warning system of the not pauAwa'Le very distant future will dramatically slice the time between the occurrence of a tsunami- generating earthquake and the issuance of watches and warnings by Honolulu and the regional systems. ge These and other uses of space age tech- nology have been accompanied by a con- tinuing effort to improve tsunami detection, predicton, and theory. The Joint Tsunami Research Effort, a cooperative venture of NOAA's Environmental Research Laborato- ries and the University of Hawaii, has been pursuing the legion unknowns of the great waves since the mid-1960's. One reason there are still so many unan- swered questions about tsunamis is that they are difficult to observe directly. They leave their tidal record and their mark on coastal communities, and that is about all. So that tsunami research has involved a good deal of detective work. The researchers have set up a volunteer get good observer program, in an effort to time-lapse photography and measurements of tsunami water-levels and run-up. This obser vation program also tries to correlate ground deformation and other effects and eye-wit- ness accounts in the event of a tsunami. The group has fielded some new tsunami- sensing equipment, including the offshore pressure-sensors used in the Hawaiian re- gional warning system. These measure the changes in the height of the water column above the sensor caused by a passing tsu- nami or other wave of that amplitude and period. An electromagnetic wave-measuring technique developed there uses the interac- tions of ocean waves with an electromagnetic field to sense tsunami's wave action offshore; it has also been applied to measuring tides Later in the decade of the 1970's, the first on the open ocean as part of the Mid-Ocean Geostationary Operational Environmental Sat- Dynamics Experiment. ellite will be lofted into an earth-synchronous One of the key efforts at the laboratory in- orbit above the International Dateline. This volves the development of mathematical mod- spacecraft, like its geostationary predeces- els which simulate the behavior of tsunamis. sors, will seem to mark time 22,300 miles Using present models, the NOAA scientists S A above a point on the equator; and, like its are looking into such unseeable events as predecessors, it will provide a relay point for tsunami generation, deep-ocean propagation, a wide spectrum of fast-moving environmen- and the relationship between the source of tal data, including tsunami watches and warn- a tsunami and the shape taken by the mature ings. wave series. 16 Computer models at NOAA's Joint Tsunami Research Effort (with the University of Hawaii) are being used to sim. ulate tsunami generation, open-ocean propagation, run-up, and other characteristics. Here, a simulated tsunami spreads from the March 1964 Alaska epicenter. 17 HEM NOAA scientists have developed a series of tsunami ------- travel-time charts, computed to provide wave travel-times 77@ from any Pacific earthquake epicenter to a number of selected- I z coastal locations. In the -- - -------- charts reproduced here, for example, a tsunami generated by an earthquake near the Philippines would be felt at Midway Island in about seven and a half hours, and, at Kodiak, Alaska, in about fourteen and a half hours. 7 0- 18 suna L FETY LE 01 look,._ Tsunamis are the so-called "tidal waves" 6. The Tsunami Warning System does not generated by some earthquakes. When you issue false alarms. When an ocean-wide hear a tsunami warning, you must assume a warning is issued, a tsunami exists. When a dangerous wave is on its way. History shows regional warning is issued, a tsunami prob- that when the great waves finally strike, they ably exists. The tsunami of May 1960 killed claim those who have ignored the warning. 61 in Hilo, Hawaii, who thought it was "just 1. All earthquakes do not cause tsunamis, another false alarm." but many do. When you hear that an earth- 7. All tsunamis-like hurricanes-are po- quake has occurred, stand by for a tsunami tentially dangerous, even though they may emergency. not damage every coastline they strike. 2. An earthquake in your area is a natural B. Never go down to the beach to watch tsunami warning, Do not stay in low-lying for a tsunami. When you can see the wave coastal areas after a local earthquake. you may be too close to escape it. 3. A tsunami is not a single wave, but a 9. Sooner or later, tsunamis visit every series of waves. Stay out of danger areas coastline in the Pacific. Warnings apply to until an "all-clear" is issued by competent you if you live in any Pacific coastal area. authority. 10. During a tsunami emergency, your 4. Approaching tsunamis are sometmes local Civil Defense, police, and other emer- heralded by a noticeable rise or fall of coastal gency organizations will try to save your life. water. This is nature's tsunami warning and Give. them your fullest cooperation. should be heeded. Stay tuned to your radio or television sta- 5. A small tsunami at one beach can be a tions during a tsunami em&rgency-builetins giant a few miles away. Don't let the modest issued through Civil Defense and NOAA of- size of one make you lose respect for all. fices can help you save your life! 19 U.S. GOVERNMENT PRINTING OFFICE : 1975 0 - 588-132 NOAA 01@ &N I of Documents, U.S. Government Printing Office C. 20402 - Price 55 cents Number 003-017-00322-1 3 6668 00000 3543