The December 2004 earthquake off Sumatra was the second largest earthquake ever recorded (only a 9.5 earthquake off of Chile in 1960 was bigger). It occurred where part of the ocean floor was thrust upwards by the movement of the India plate under the Burma Plate off the northwest coast of Sumatra, where the India plate and Australian plate dive under Burma at the Sundra Trench plate. During the quake a section of one plate about 700 miles long suddenly plunged about 30 feet beneath another

The tsunami was so large in part because the movement on the fault was vertical not horizontal and the earthquake did not occur on a single point of the fault as is usually the case with an earthquake but occurred along a 1,200 kilometer length of the fault. In some places the seabed lifted four meters. Movement started off the coast of Sumatra and moved northward along the fault at a rate of around two kilometers per second.

The December 2004 earthquake was so powerful it temporarily shifted the earth on its axis about 2.5 centimeters, caused the earth to spin 3 microseconds faster, lifted the ground by two centimeters as far away as Ecuador and produced the energy equivalent of 1 million Hiroshima bombs. The entire west coast of Sumatra moved. Near the epicenter islands were raised higher out of the sea and moved 100 feet to the southeast. Buildings swayed as far away as Bangladesh and Chiang Mai in northern Thailand. Seismic waves produced by the earthquake traveled around the earth three times. An observatory in Japan recorded the first set of waves at 10:20am, the second set around 12:55pm and the third set around 3:55pm.

Geology of the Earthquake That Triggered the Great Tsunami of 2004

The earthquake struck along the Sumatra-Andaman fault along the coast of Sumatra and islands to the north. Here the Indo-Australian plate steadily pushes northward and, at the same time, thrusts under the Eurasian plate. The two plates converge here at a rate of three or four centimeters a year, building up immense stresses at the boundary. Large earthquakes have been recorded here since 1797, though none as massive as the one in 2004. [Source: Dave Fore Natural History magazine, September 2005]

Natural History magazine reported: “On the day of the great earthquake the plate boundary, which is normally locked up by the pressure and friction of the rock masses, gave way near the northern tip of Sumatra, about 30 kilometers below the surface of the sea. It was almost as if a zipper had suddenly became unzipped. Within the next minute a 100 kilometer stretch of seafloor north of the initial rupture slipped rapidly beneath Sumatra. In the next eight or nine minutes the rupture raced northward for nearly 1,600 kilometers along the plate boundary. The seafloor instantly buckled above the rupture and a vast area rose up several meters while areas to the east and west of the rupture sank. This contortion of the seafloor displaced millions of tons of seawater, initiating the tsunami.

“Then, as vibrations spread through the surrounding rock, the rate at which the two plates had been slipping past one another slowed dramatically. About a half an hour later the slippage stopped. Altogether, a total displacement of the seafloor made quake a 9.15 magnitude event...But, its effects did not stop there. In March 2005, another 300-kilometer-long segment of the plate boundary failed, adjacent to the December rupture. Now the global sea level is half a millimeter higher because of the massive jolt.

Power of the December 2004 Earthquake Off Sumatra

On the enormous energy released by the December 2004 quake, AP reported: The great Sumatra-Andaman earthquake that generated the devastating tsunami in December was so powerful that the ground shook everywhere on the Earth's surface and weeks later the planet still trembled. "No point on Earth remained undisturbed," said Roger Bilham of the University of Colorado. Ground movement of at least 0.4 inch occurred everywhere as a result of the strongest quake in more than 40 years, though the sensation was not noticed in many areas. [Source: AP, May 19, 2005]

The energy released by the Indian Ocean earthquake is estimated to have been the equivalent of 23,000 Hiroshima-sized atomic bombs — that’s nearly three Hiroshimas for every mile of affected coastline. “The quake resulted from the longest fault rupture ever observed “720 miles (1160 kilometers) to 780 miles (1255 kilometers) , which spread for 10 minutes. A typical earthquake lasts for 30 seconds. The quake was the first of its size to be measured and studied by the new worldwide array of digital seismic instruments. A special section of a half-dozen research papers on the quake appeared in a issue of the journal Science. "This is really a watershed event. We've never had such comprehensive data for a great earthquake because we didn't have the instrumentation to gather it 40 years ago," said Thorne Lay, professor of earth sciences and director of the Institute of Geophysics and Planetary Physics at the University of California, Santa Cruz. "It is nature at its most formidable," Lay said in a statement.

“The quake occurred where two of the giant plates that form the surface of the Earth grind together. At that spot, the Eurasian plate was being pulled downward by the descending Indo-Australian plate. The quake released the edge of the Eurasian plate, which sprang up, lifting the ocean floor and sending the sea water off in the giant wave, the researchers reported. They said the higher sea floor displaced so much water from the Bay of Bengal and the Andaman Sea that sea level worldwide was raised by 0.004 inch.

“The temblor also "delivered a blow to our planet" that was felt for weeks, according to a team of researchers led by Jeffrey Park of Yale University. His group calculated that the quake caused the planet to oscillate like a bell, at periods of about 17 minutes, which scientists were able to measure for weeks afterward. A similar phenomenon was first noted in a 1960 quake in Chile. The initial quake off Sumatra on Dec. 26 is estimated to have had a magnitude of 9.1 to 9.3. A second quake to the south on March 28 registered 8.6. By comparison, the 1960 Chile earthquake was magnitude 9.5 and the one in Alaska in 1964 was 9.2. California's 1989 Loma Prieta earthquake had a magnitude of 6.9.

“Among the other findings reported in the various papers: 1) In Sri Lanka, more than 1,000 miles from the epicenter, the ground moved nearly 4 inches. 2) The rupture spread from south to north. Seismometers in Russia recorded the quake at a higher frequency because it was moving toward them, while those in Australia measured a lower frequency as it moved away. 3) When the surface waves from the Sumatra quake reached Alaska they triggered a swarm of 14 earthquakes in the Mount Wrangell area.

In addition to Lay, Bilham and Park, the lead authors of the articles were Charles J. Ammon of Pennsylvania State University, Michael West of the University of Alaska and Roland Burgmann of the University of California, Berkeley. Burgmann's article was published in Science Express, the journal's online edition. The various researchers were supported by the National Science Foundation, U.S. Geological Survey, Incorporated Research Institutions for Seismology, NASA Jet Propulsion Laboratory, California Institute of Technology Tectonics Observatory, Geoscope Program-IPGP France, Alaska Earthquake Information Center, Alaska Volcano Observatory, Geophysical Institute of the University of Alaska and the Alaska Division of Geological and Geophysical Surveys.

December 2004 Earthquake Shook Gravity and Caused Earth to Ring Like a Bell

After the December 2004 earthquake and tsunami, Reuters reported: “Two weeks on, the earth is still vibrating from the massive undersea earthquake off Indonesia that triggered the tsunami, Australian researchers said on Sunday. The Australian National University (ANU) said the reverberations were similar in form to the ringing of a bell, though without the sound, and were picked up by gravity monitoring instruments. [Source: Reuters, January 10, 2005]

“These are not things that are going to throw you off your chair, but they are things that the kinds of instruments that are in place around the world can now routinely measure, said ANU Earth Sciences researcher Herb McQueen. It is certainly above the background level of vibrations that the earth is normally accustomed to experiencing. The magnitude 9.0 earthquake, the strongest for 40 years, struck off the coast of Indonesia's Sumatra island on December 26. The tsunami it generated claimed more than 156,000 lives.

“Mr McQueen said the oscillation was fading and at current levels equated to about a millimetre of vertical motion of the earth. Immediately after the quake the oscillation was probably in the 20 to 30 cm motion range that is typically generated in the earth by the movements of the sun and moon. This particular earthquake because it was 10 times larger than most of the recent large earthquakes is continuing to reverberate, Mr McQueen said. “We can stil see a steady signal of the earth vibrating...From what it looks like, it appears it will probably continue to oscillate for several more weeks,” he said.

The New York Times reported: The giant earthquake that set off a devastating tsunami across the Indian Ocean in December 2004 disrupted the earth enough to change gravity and to deflect satellites passing hundreds of miles above. Two identical satellites, collectively known as the Gravity Recovery and Climate Experiment, or Grace, travel one behind the other in a polar orbit separated by about 130 miles. By recording small changes in the distance between them when their orbits are deflected, the satellites provide data used to calculate variations in the earth’s gravitational field. [Source: New York Times, August 8, 2006]

“In a report in the journal Science, scientists at Ohio State University and the University of California, Santa Barbara recorded a sudden drop in gravity near the quake’s epicenter off Sumatra. The rupture raised thousands of square miles of the seafloor, reducing the density of rocks in the earth’s crust and diluting their gravitational pull. The data, combined with models of the earth’s interior, indicate that the density changes extend hundreds of miles. “It really gives an insight of the earth’s interior down to the mantle area,” said Shin-Chan Han, an Ohio State research scientist and an author of the Science paper. It was the first time that the gravitational effect of an earthquake had been observed from space.

“The gravity at the earth’s surface decreased by as much as about 0.0000015 percent, meaning that a 150-pound person would experience a weight loss of about one-25,000th of an ounce. In other places, where the force of the earthquake compressed rocks, gravity increased by a similar amount. The force of gravity is changing in other areas of the earth, too. In Hudson Bay, Canada, which was crushed downward by the weight of ice during the last ice age, the ground is still rebounding upward. That change adds about one-400,000th of an ounce to the weight of a 150-pound person every year.

Details of the Great Tsunami of December 2004

The earthquake occurred in deep water. There was an upwards movement of the sea floor towards the north of a few meters. Because there was so much water on top of and so much pressure, the energy released was enormous. Minutes after the earthquake, the tsunami split, producing pulses of waves that moved both east and west. The earthward-moving wave traveled with trough first, pulling water away from the shore, while the one heading west traveled crest first.

As is true with most tsunamis the waves radiated out in directions opposite from the seismic disturbance. The earthquake-generating fault ran north-to-south while the tsunamis moved east and west. That is why Bangladesh suffered relatively little damage while Sri Lanka got walloped. A 1,120-kilometer section of sea floor — extending northward from the epicenter past northern Sumatra and into the Nicobar and Andaman Islands of India — shifted, moving as much as 20 meters in some places. This explains why so much water was displaced so suddenly, proding a large tsunami, and why the tsunami hit places like southern Thailand and northern Malaysia that appeared to have been blocked from the epicenter of the earthquake by Sumatra.

The waves of the tsunami raced across the Indian Ocean at speeds up to 700 kilometers per hour and reached a height 15 meter in some places. The backwash reached speeds of 350 kilometers per hour. In Indonesia and Thailand, where the water near the shore is relatively shallow, the waves crashed ashore like large Hawaiian waves except they surged inland. In Sri Lanka and India, where the water is deeper the waves were in the form of surges that poured water inland like quick, surging tides. On Mauritius and Diego Garcia — islands in the Indian Ocean — the tsunami barreled right past, causing very little damage.

The waves reached the west coast of Sumatra within minutes after the earthquake and Thailand 30 minutes to an hour later. They reached Sri Lanka and India in about two hours, the Maldives in 3½ hours and Africa in six hours. In some cases waves reached islands of India before they reached Thailand. This is because the sea around the west of Thailand is relatively shallow, which slowed the waves down considerably.

The largest waves that hit Sumatra were 25 meters high. Three-meter waves hit Kenya, Tanzania and Somalia, where dozens of people were killed. Three-meter waves hit the Americas. A “train” of 22-centimeter-high waves produced by the tsunami reached the east coast of the United States 32 hours after the earthquake.

According to the Christian Science Monitor: Tsunamis are typically the devastating handiwork of quakes known as subduction earthquakes. They're the most powerful earthquakes on the planet, and they occur at plate boundaries, where one tectonic plate is grinding inexorably beneath another. When the bottom plate suddenly lurches deeper, a colossal amount of energy is released, unleashing the sorts of massive earthquakes and calamitous tsunamis that hit the Indian Ocean in 2004 and the coast of Japan in March 2011.

Aftershocks and Earthquakes After the Great Tsunami of 2004

A number of strong aftershocks shook Indonesia in the months after the December 2004 tsunami-generating quake. There were more than dozen temblors over 6.0. Some forced governments to issue tsunami warnings and sent people running in panic in fear another killer tsunami.

On March 28, 2005, A "great" earthquake struck the Banyak, Nias and Simeulue Islands off the west coast of Sumatra. ASC reported on its website: The earthquake had a magnitude of 8.7 on the Richter scale and caused considerable damage to life & property in the region. A damaging local tsunami was generated in the vicinity of earthquake adding to the damage. This earthquake was initially believed to have been a large aftershock from the 2004 Sumatra-Andaman earthquake that occurred to the north. It has since been determined to have been triggered due to changes in the static stress regime of the region brought about by the 2004 event and was thus not a large aftershock. [Source: ASC (Amateur Sesmic Center), Pune India]

“The earthquake was centered nine kilometers west of Teluk Asin, Pulau Bangkaru (Sumatra), Indonesia. According to a report by the government of Indonesia's agency for Reconstruction and Rehabilitation, 839 people were killed and 6,279 others were injured in this earthquake. The island of Nias was hardest hit badly damaging several villages and the large towns of Gunungsitoli and Telukdalam. Eyewitness said the shaking was so severe that people could not stand. Damage also occurred on the island of Simeulue and in the town of Sinabang in the southern part of the same island. Parts of the Banyak Islands sank by as much as 3-feet while parts of Nias such as Lagundri Bay were uplifted. Damage was also reported at Gunung Meriah, Meulaboh, Samatiga, Simpang Kiri, Singkil and in the Tapanauli regency on Sumatra. The earthquake was strongly felt in Banda Aceh, Lhokseumawe, Medan and in the Bireuen Regency on Sumatra. It was also felt at Bengkulu, Jambi, Krui, Padang, Pekanbaru and Riau. At Banda Aceh, the shock was experienced for nearly 75-seconds. People had some difficulty standing and eyewitness saw cars and trucks shaking under the impact of the quake. Panic followed once the shaking ended and hundreds of people fled to higher ground, using any means available. Similar scenes of panic were witnessed at Medan and in other cities in Sumatra.

“In Thailand, the earthquake was felt in many parts of the country. High rise buildings in the capital, Bangkok and in the city of Hat Yai were temporarily evacuated. In areas hard hit by the December 2004 tsunami such as Khao Lhak, Krabi, Nakhon si Thammarat, Satun and Songhkla, people immediately began moving to higher ground once they felt the earthquake. A few buildings in Hat Yai and Songhkla suffered minor damage. In Malaysia, the earthquake was felt along the entire west coast including at Johor, Kedah, Kuala Lumpur, Langkawi, Muar, Penang, Petaling Jaya, Pontian, Port Klang, Tanjung Pelepas and Tanjung Piai. Tremors were felt in high-rise buildings in Alexandra, Bekor, East Coast, Punggol, Rochor, Sengkang, Toa Payoh, Whampoa, Woodlands in Singapore. Strong tremors were felt in the Nicobar Islands in India. Farther north the quake was mildly felt by the occupants in the upper floors of buildings in Diglipur & Port Blair in the Andaman Islands. Tremors from this earthquake were not felt on the Indian mainland. However, seismic seiches were observed in ponds & standing water bodies at Basanti, Canning, Kolkata and Kulpi in West Bengal. Mild tremors from the earthquake were felt along the east coast of Sri Lanka and as far as the Maldives.

“A damaging local tsunami struck Banyak, Nias, Simeulue and the west coast of Sumatra following the earthquake. Fearing another tsunami thousands of people fled to higher ground in Banda Aceh and other parts of coastal Sumatra, Indonesia. A boat off the Banyak Islands experienced strong swells and unusual currents for as long as two hours after the earthquake. A local tsunami struck Nias Island with wave heights of 4-5 metres and swept away many people at Sirombu. A 3-4 metre wave struck the islands of Banyak and Simeulue and the Sinkil district on Sumatra. At Sinkil, residents reported a waves of 4-metres, causing flooding upto a metre high in some parts. A 2-metre wave struck the village of Sirombu on the west coast of Nias sweeping away a few people. Flooding upto a metre was also reported from as far north as Meulaboh. The south coast of the island of Simeulue was struck by a 3-metre tsunami causing moderate damage to the port and airport facilities on Simeulue Island and resulted in at least 100 deaths. On Sumatra, the tsunami flooded parts of the towns of Meulaboh, Sigli and Singkil. At Singkil, a tsunami, reported to have been up to 4-metres high damaged many buildings. At Meulaboh, the sea receeded, drawing out the water from the river and then returned to flood coast.

“The earthquake did not generate an Indian Oceanwide tsunami although measurable changes were recorded at many places in the Indian Ocean basin. Tsunami warnings were issued for many countries in the region including India and Sri Lanka but were later withdrawn. In Sri Lanka, the National Aquatic Resource & Development Agency reported waves with a maximum height of 2.3 metres at Kirinda in southern Sri Lanka. According to the Pacific Tsunami Warning Centre (PTWC) tide gauges in the Indian Ocean recorded minor wave activity in the Australian Cocos Island (4-9 inches), the Maldives (6-inches) and Sri Lanka (10-12-inches). There were reports of the sea receeding at several places along the coast of Chennai, Mamalapuram and Tuticorin in Tamil Nadu and Machilipatnam in Andhra Pradesh in India.

“Thousands of people in India, Indonesia, Malaysia, Sri Lanka and Thailand were either evacuated to safer places or fled of their on accord to higher grounds. In Sumatra, roads leading out of Banda Aceh were jammed with vehicles and people trying to flee the city. Similar scenes were repeated across the region. In Sri Lanka, residents of Colombo, Trincomalee and other coastal areas were advised to more away from the coast as a precaution. At least 5 deaths were reported from Sri Lanka. These were the result of road accidents or heart attacks due to panic driven escapes by the population to higher ground at places such as Mavadippalli and Kalmunai. Hundreds of people fled to higher ground at places such as Batticaloa and Vadamaradhhi East. The residents of the Maldives were also advised to remain on alert for possible tsunami activity. In India, the Andaman & Nicobar Islands and the coastal areas of the mainland states of Andhra Pradesh, Kerala, the Lakshadweep Islands, Pondicherry and Tamil Nadu were alerted. In Chennai, roads leading to beachfront areas including the Marina Beach were cordoned of. In Thailand, many people immediately moved to higher ground in places such as Khao Lhak, Koh Phi Phi, Krabi, Patong Beach, Phang Nga, Phuket, Satun, and Takua Pa, Trang and similar scenes were witnessed at Kedah, Langkawi, Penang & Perlis in Malaysia. Alerts were issued in countries as far as Kenya and Madagascar in east Africa and in the island nation of Mauritius.

Great Tsunami of 2004 and the Aftershocks and Earthquakes That Followed It

Rob Stein wrote in the Washington Post: The massive earthquake on March 28 in the Nias Islands area of Sumatra “occurred in a region that is prone to temblors because large segments of Earth's crust are colliding there, creating enormous pressures that are released periodically in cataclysmic jolts, geologists said yesterday. Scientists had been expecting that another large quake might strike soon in the region because the massive undersea upheaval that triggered December's tsunami generated even more pressure on the region's already volatile geology, experts said. [Source: Rob Stein, Washington Post, March 29, 2005]

"What happened today was not a surprise. A number of scientists have been talking about an increased likelihood of more earthquakes in this area because of the rupture that happened in December," said Lori Dengler, a geologist at Humboldt State University in Arcata, Calif. "And it may not stop here." Earthquakes occur along the boundaries between sections of Earth's surface known as plates. These plates are constantly moving, slowly but inexorably pushing against one another. "They are squeezing together over geologic time at about the rate your fingernails grow," said Alan L. Kafka, a geophysicist at Boston College. "The movement causes tremendous amounts of force to build up and up and up." Eventually, rock in one of the plates gives way under the pressure, causing a section to snap and the plates to suddenly lurch.

"It's on these plate boundaries that we have the world's largest earthquakes," said Bruce Presgrave, a geophysicist at the U.S. Geological Survey's National Earthquake Information Center. "The rocks are stressed and stressed and stressed until finally they can't sustain it anymore and they snap, shifting to a new position. That's what we feel as earthquakes." The area where the March 28, 2005 quake occurred is particularly troublesome because of the speed at which plates there are converging, and their relative positions. Unlike the San Andreas fault in California, where two plates are moving past each other horizontally, the region west of the island of Sumatra is a "subduction zone," where plates are sliding over and under one another. "These are the places where we have most of the world's earthquakes, and lots and lots of volcanoes," Dengler said.

“The December 26, 2004 quake p robably increased pressure on the next section of the plate boundary just to the south, causing yesterday's similar sudden thrust of one plate beneath the other, this time apparently involving a smaller section of perhaps 200 to 300 miles. "We think it's very likely that the extra stresses put on by the quake happening to the northwest is very likely to have triggered this earthquake. It would have happened sometime, but the timing may have been moved up by the quake to the north," Presgrave said.

“There is now an increased possibility that yet another massive quake could occur soon, farther along the same plate boundary, experts said. "Think of a crack in your windshield that propagates over time," said Kate Hutton, a seismologist at the California Institute of Technology. "Once there's a break, the two ends are the most highly stressed and it eventually keeps growing." The timing of the next event is unpredictable because it depends on a host of factors, including whether pressure had been released along the boundary by previous quakes. But more quakes are inevitable. "It's just a question of when, and how big," Dengler said.

“Scientists were unsure yesterday why this quake apparently did not cause a tsunami, but there could be a number of explanations. If the temblor caused the seafloor only to vibrate, instead of suddenly shifting upward, that would have prevented a tsunami. "The question is whether it actually shifted the seafloor itself. If the quake doesn't actually move the seafloor, and just shakes it, then you're not moving the water," Presgrave said. Another possibility is that the force of whatever water movement occurred was dissipated by nearby islands or just moved out to sea. But scientists are studying the event for clues that might help them predict future tsunamis.

December 2004 Sumatra Connected to Strange April 2012 Earthquake

In September 2012, the Christian Science Monitor reported: On the afternoon of April 11, 2012, one of the most powerful earthquakes ever recorded — and now revealed to be among the weirdest — struck in the Indian Ocean, off the coast of Sumatra...Eight years earlier, in December 2004, the third largest earthquake on record had ripped through a nearby region of the ocean floor. The magnitude-9.1 earthquake and the monstrous tsunami that soon followed killed more than 227,000 people in 14 countries. [Source: Andrea Mustain, OurAmazingPlanet, September 27, 2012]

“So when a magnitude-8.7 earthquake (some put the magnitude at 8.6) shook the Indonesian island on that Wednesday afternoon earlier this year, many expected the worst. Yet, no monster wave appeared. A wave did come ashore, but it was a miniature tsunami, just 12 inches (31 centimeters) high. All told, the earthquake did very little damage — yet only five higher earthquake magnitudes have ever been recorded. So what was the deal?

“New research published in September 26, 2012 in the journal Nature delves into the intimate details of this earthquake, along with the powerful, magnitude-8.2 quake that followed two hours later. The new studies add to an existing body of research that shows this was a remarkable event — one of the most surprising earthquakes ever recorded — and one that offers an unlikely snapshot of a geological process millions of years in the making.

“The April 11 earthquake was the most powerful strike-slip quake ever recorded. Not only was the quake of unparalleled power, it hit in the middle of a tectonic plate, not at a plate boundary, like the San Andreas Fault. "So already it has two unusual attributes," said Thorne Lay, a professor of earth and planetary sciences at the University of California, Santa Cruz, and an author on one of the papers published today. Lay and his team set out to construct a blow-by-blow account of how the earthquake progressed, and what they found added to the quake's mystique. This earthquake was able to turn corners. "It's totally unusual," Lay told OurAmazingPlanet. It turns out that the quake began on one fault, streaking along at more than a mile per second, and, when it reached an intersecting fault, it ruptured that one, too. In all, it ruptured four different faults over the course of 150 seconds, unleashing an amount of energy equivalent to about four magnitude-8.0 earthquakes.

“Lay said that, typically, when earthquakes spread to connecting faults, the rupture rips along faults that branch away from the initial fault like the branches of a river. These earthquakes raced along in a grid-like pattern, making 90-degree turns along faults that resemble a lattice."Here, they really do seem to go along perpendicular faults, and we haven't seen anything like that with a big earthquake," he said. However, he said, the weird rupture pattern reflects the weird geological circumstances at play in the neighborhood where the earthquake hit. The April 11 earthquake occurred in a region that is giving birth to the Earth's newest tectonic plate.

Did the December 2004 Sumatra Earthquake Launch a New Tectonic Plate?

In September 2012, the Christian Science Monitor reported: “The earthquake hit in the middle of the Indo-Australian plate, a plate that is being torn asunder. And in fact, it is this process that helped trigger this astonishingly powerful earthquake. In a way, the area where it hit was primed for a major earthquake — scientists just had no idea how major such an earthquake could be. "It's a pre-existing zone of weakness," said Matthias Delescluse, a marine geophysicist at Paris's Ecole Normale Supérieure and an author of another Nature paper on the earthquake published today. [Source: Andrea Mustain, OurAmazingPlanet, September 27, 2012]

“The faults that the earthquake ruptured are, essentially, the bones of an ancient volcanic seam that once snaked across the ocean floor, giving rise to new crust. The system fell silent 45 million years ago, but the fractures it created in the tectonic plate are still there. And this particular tectonic plate is undergoing some major stress, Delescluse told OurAmazingPlanet. "I like to represent it with the sidecar analogy," he said. Think of the Australia region of the plate as a motorbike, and the India region as a sidecar. Both are hurtling northward at a fast clip — for a tectonic plate at least — at about 2 inches (5 cm) per year. "Now imagine the sidecar — not the motorbike — runs into a wall," Delescluse said. "The sidecar would compress, and the motor bike, depending on the violence of the shock, would finally detach from the sidecar."

“That wall that our India sidecar is hitting is the Eurasian plate. The colossal collision has produced some impressive side effects: the Himalayas, the highest mountains on Earth. Australia is able to continue its progress largely unhindered, because that portion of the plate is diving under another tectonic plate — a process that produces the sort of massive earthquake that hit in 2004.

“The evidence suggests that the Indo-Australian plate began to be ripped apart between 8 million and 10 million years ago. The 2012 earthquake is just one of many that have likely ripped along the same region since this process began. After millions more years of similar earthquakes, the ruptures will begin to favor a particular path, giving rise to a new plate boundary, and separating today's existing plate into two. Delescluse said that the singular earthquake measured in 2012 offers a glimpse of this process in unprecedented detail. "This event is really illustrating what happened in the past and will happen in the future," he said.

"The fact that within six months we have understood this much — that is really quite impressive," said Hiroo Kanamori, a professor emeritus at Caltech, and a revered figure among geophysicists. He was not involved in the research. Kanamori, who has studied large earthquakes for decades, said that vast improvements in both the quality and quantity of instruments, and of methodology, has allowed the science to make unprecedented strides forward.

"If this had happened 40 years ago, it would have taken a few years to even understand what it was," he told OurAmazingPlanet. And although he said the event certainly was surprising, he noted that it's only surprising from the perspective of a human lifetime — "not on the geological time scale," he said. Lay echoed Kanamori's long-term perspective."When you're dealing with a process that may be taking millions of years, we're getting a very short window of observation from which to make generalizations about the past," he said. "Astronomers can look farther away, and they can see farther back in time — we see what we see today," he said. And the Earth may have more geological surprises in store, he said.

Tsunamis in Indonesia

Between 1992 and the 2003, 17 major tsunamis struck worldwide, 11 in the Pacific. Fatalities were relatively low, a total of some 4,000. Places most vulnerable to tsunamis (number expected in the next 100 years): 1) Japan (38); 2) New Guinea (15); 3) Indonesia (13); 4) Hawaii (12); 5) Chile (9); 6) Alaska (7); 7) Australia (6).

Earthquakes on Sundra Trench faults generated killer tsunamis in 1833 and 1861. A tsunami in 1992, washed away two thirds of an Indonesian island. A tsunami struck Java in 1994.

The December 2004 earthquake and tsunami occurred along a fault with segments under the Batu and Mentawai islands. AP reported: “The Batu-Mentawai area produced a large earthquake in 1833, triggering a tsunami that devastated the adjacent coast of Sumatra. But because of the quake's location, most of the tsunami's energy flowed out into the open Indian Ocean. It passed south of Sri Lanka and India, which were hit hard by the Dec. 26 tsunami.

See Krakatoa

Image Sources: Wikimedia Commons

Text Sources: New York Times, Washington Post, Los Angeles Times, Times of London, The Guardian, National Geographic, Smithsonian magazine, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Wall Street Journal, The Atlantic Monthly, The Economist, Global Viewpoint (Christian Science Monitor), Foreign Policy, Wikipedia, BBC, CNN, NBC News, Fox News and various books and other publications.

Last updated November 2012

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