Misplaced Pages

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124-545: Adjacent to the UMCU lies the Central Military Hospital, or CMH, for military personnel. The UMCU also features a Major Incident Hospital (Dutch: Calamiteitenhospitaal ). This facility is intended for treating groups of more than five military or civilian casualties in case of major catastrophes, war casualties or in case of particular contagious diseases (for example, repatriated wounded Dutch citizens after

248-663: A line source ). This greatly increased the geographical area over which the waves were observed, reaching as far as Mexico, Chile, and the Arctic. The raising of the seafloor significantly reduced the capacity of the Indian Ocean, producing a permanent rise in the global sea level by an estimated 0.1 mm (0.004 in). Numerous aftershocks were reported off the Andaman Islands , the Nicobar Islands and

372-466: A 2.6 m (8.5 ft) crest-to-trough tsunami was measured. As well, the tsunami was large enough to be detected in Vancouver , which puzzled many scientists, as the tsunamis measured in some parts of South America were larger than those measured in some parts of the Indian Ocean. It has been theorized that the tsunamis were focused and directed at long ranges by the mid-ocean ridges which run along

496-416: A body-wave magnitude scale ( mB ) by Gutenberg and Richter in 1956, and a number of variants – to overcome the deficiencies of the M L   scale, but all are subject to saturation. A particular problem was that the M s   scale (which in the 1970s was the preferred magnitude scale) saturates around M s  8.0 and therefore underestimates the energy release of "great" earthquakes such as

620-480: A busload of vacationers and locals to safety on higher ground. Anthropologists had initially expected the aboriginal population of the Andaman Islands to be badly affected by the tsunami and even feared the already depopulated Onge tribe could have been wiped out. Many of the aboriginal tribes evacuated and suffered fewer casualties, however. Oral traditions developed from previous earthquakes helped

744-618: A causal relationship between these events. The 2004 Indian Ocean earthquake is thought to have triggered activity in both Leuser Mountain and Mount Talang , volcanoes in Aceh along the same range of peaks, while the 2005 Nias–Simeulue earthquake sparked activity in Lake Toba , a massive caldera in Sumatra. The energy released on the Earth's surface ( M e , the energy magnitude, which

868-504: A constant term ( W 0 / M o  = 5 × 10 ) in Eq. (A) and estimated M s and denoted as M w (dyn.cm). The energy Eq. (A) is derived by substituting m  = 2.5 + 0.63 M in the energy equation Log E  = 5.8 + 2.4 m (Richter 1958), where m is the Gutenberg unified magnitude and M is a least squares approximation to the magnitude determined from surface wave magnitudes. After replacing

992-516: A day later. In April 2016 the Healthcare Inspectorate placed the UMCU on warning for poor healthcare and under increased supervision, after it was revealed that additional fatal incidents had been covered up. In July 2016 it was revealed that in 2015 six patients had developed an eye infection following an eye surgery at the UMCU. Four of these six patients have gone blind and hold the UMCU responsible. The UMCU had to close one of

1116-403: A distance of approximately 100 to 600 km (62 to 373 mi), conditions where the surface waves are predominant. At greater depths, distances, or magnitudes the surface waves are greatly reduced, and the local magnitude scale underestimates the magnitude, a problem called saturation . Additional scales were developed – a surface-wave magnitude scale ( M s ) by Beno Gutenberg in 1945,

1240-500: A double couple, but not from a single couple. This was confirmed as better and more plentiful data coming from the World-Wide Standard Seismograph Network (WWSSN) permitted closer analysis of seismic waves. Notably, in 1966 Keiiti Aki showed that the seismic moment of the 1964 Niigata earthquake as calculated from the seismic waves on the basis of a double couple was in reasonable agreement with

1364-479: A few mosques remained standing. The greatest run-up height of the tsunami was measured at a hill between Lhoknga and Leupung , on the western coast of the northern tip of Sumatra, near Banda Aceh, and reached 51 m (167 ft). The tsunami heights in Sumatra: The island country of Sri Lanka, located about 1,700 km (1,100 mi) from Sumatra, was ravaged by the tsunami around two hours after

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1488-418: A general solution in 1964 by Burridge and Knopoff, which established the relationship between double couples and the theory of elastic rebound, and provided the basis for relating an earthquake's physical features to seismic moment. Seismic moment – symbol M 0   – is a measure of the fault slip and area involved in the earthquake. Its value is the torque of each of the two force couples that form

1612-442: A landmass between them and the tsunami's location of origin are usually safe; however, tsunami waves can sometimes diffract around such landmasses. Thus, the state of Kerala was hit by the tsunami despite being on the western coast of India, and the western coast of Sri Lanka suffered substantial impacts. Distance alone was no guarantee of safety, as Somalia was hit harder than Bangladesh despite being much farther away. Because of

1736-453: A large turbulent bore. Eyewitnesses described the tsunami as a "black giant", "mountain" and a "wall of water". Video footage revealed torrents of black water, surging by windows of a two-story residential area situated about 3.2 km (2.0 mi) inland. Additionally, amateur footage recorded in the middle of the city captured an approaching black surge flowing down the city streets, full of debris, inundating them. The level of destruction

1860-441: A low, broad hump, barely noticeable and harmless, which generally travels at the high speed of 500 to 1,000 km/h (310 to 620 mph); in shallow water near coastlines, a tsunami slows down to only tens of kilometres per hour but, in doing so, forms large destructive waves. Scientists investigating the damage in Aceh found evidence that the wave reached a height of 24 m (80 ft) when coming ashore along large stretches of

1984-612: A magnitude of 9.2–9.3 M w struck with an epicentre off the west coast of northern Sumatra , Indonesia. The undersea megathrust earthquake , known by the scientific community as the Sumatra–Andaman earthquake , was caused by a rupture along the fault between the Burma plate and the Indian plate , and reached a Mercalli intensity of IX in some areas. A massive tsunami with waves up to 30 m (100 ft) high, known as

2108-401: A magnitude of as high as 6.9 ) and presently ranks as the third-largest earthquake ever recorded on the moment magnitude or Richter scale . Other aftershocks of up to magnitude 7.2 continued to shake the region daily for three or four months. As well as continuing aftershocks, the energy released by the original earthquake continued to make its presence felt well after the event. A week after

2232-447: A major earthquake under ordinary circumstances but is dwarfed by the mainshock . The shift of mass and the massive release of energy slightly altered the Earth's rotation. Weeks after the earthquake, theoretical models suggested the earthquake shortened the length of a day by 2.68 microseconds , due to a decrease in the oblateness of the Earth. It also caused the Earth to minutely "wobble" on its axis by up to 25 mm (1 in) in

2356-486: A month after the earthquake found the movement to be about 0.2 m (8 in). Since movement was vertical as well as lateral, some coastal areas may have been moved to below sea level. The Andaman and Nicobar Islands appear to have shifted south-west by around 1.25 m (4 ft 1 in) and to have sunk by 1 m (3 ft 3 in). In February 2005, the Royal Navy vessel HMS  Scott surveyed

2480-617: A network of sensors is needed to detect it. Tsunamis are more frequent in the Pacific Ocean than in other oceans because of earthquakes in the " Ring of Fire ". Although the extreme western edge of the Ring of Fire extends into the Indian Ocean (the point where the earthquake struck), no warning system exists in that ocean. Tsunamis there are relatively rare despite earthquakes being relatively frequent in Indonesia. The last major tsunami

2604-402: A portion Δ W {\displaystyle \Delta W} of this stored energy is transformed into The potential energy drop caused by an earthquake is related approximately to its seismic moment by where σ ¯ {\displaystyle {\overline {\sigma }}} is the average of the absolute shear stresses on the fault before and after

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2728-532: A reference point and the ten-fold (exponential) scaling of each degree of magnitude, and in 1935 published what he called the "magnitude scale", now called the local magnitude scale , labeled M L  . (This scale is also known as the Richter scale , but news media sometimes use that term indiscriminately to refer to other similar scales.) The local magnitude scale was developed on the basis of shallow (~15 km (9 mi) deep), moderate-sized earthquakes at

2852-423: A single block of rock some 100 m (330 ft) high and 2 km (1.2 mi) long. The momentum of the water displaced by tectonic uplift had also dragged massive slabs of rock, each weighing millions of tonnes, as far as 10 km (6 mi) across the seabed. An oceanic trench several kilometres wide was exposed in the earthquake zone. The TOPEX/Poseidon and Jason-1 satellites happened to pass over

2976-449: A single couple model. In principle these models could be distinguished by differences in the radiation patterns of their S-waves , but the quality of the observational data was inadequate for that. The debate ended when Maruyama (1963), Haskell (1964), and Burridge and Knopoff (1964) showed that if earthquake ruptures are modeled as dislocations the pattern of seismic radiation can always be matched with an equivalent pattern derived from

3100-439: A three-decade-long controversy over the best way to model the seismic source: as a single couple, or a double couple. While Japanese seismologists favored the double couple, most seismologists favored the single couple. Although the single couple model had some shortcomings, it seemed more intuitive, and there was a belief – mistaken, as it turned out – that the elastic rebound theory for explaining why earthquakes happen required

3224-400: Is a measure of the work (more precisely, the torque ) that results in inelastic (permanent) displacement or distortion of the Earth's crust. It is related to the total energy released by an earthquake. However, the power or potential destructiveness of an earthquake depends (among other factors) on how much of the total energy is converted into seismic waves. This is typically 10% or less of

3348-429: Is approximately related to seismic moment by where η R = E s / ( E s + E f ) {\displaystyle \eta _{R}=E_{s}/(E_{s}+E_{f})} is radiated efficiency and Δ σ s {\displaystyle \Delta \sigma _{s}} is the static stress drop, i.e., the difference between shear stresses on

3472-434: Is believed to have been a foreshock , preceding the main event by over two years. Great earthquakes, such as the 2004 Indian Ocean earthquake, are associated with megathrust events in subduction zones. Their seismic moments can account for a significant fraction of the global seismic moment across century-scale periods. Of all the moment released by earthquakes in the 100 years from 1906 through 2005, roughly one eighth

3596-505: Is complete and ignores fracture energy), (where E is in Joules and M 0   is in N ⋅ {\displaystyle \cdot } m), Kanamori approximated M w   by The formula above made it much easier to estimate the energy-based magnitude M w  , but it changed the fundamental nature of the scale into a moment magnitude scale. USGS seismologist Thomas C. Hanks noted that Kanamori's M w   scale

3720-471: Is more directly related to the energy of an earthquake than other scales, and does not saturate – that is, it does not underestimate magnitudes as other scales do in certain conditions. It has become the standard scale used by seismological authorities like the U.S. Geological Survey for reporting large earthquakes (typically M > 4), replacing the local magnitude (M L  ) and surface-wave magnitude (M s  ) scales. Subtypes of

3844-405: Is more than twice the total explosive energy used during all of World War II (including the two atomic bombs) but still a couple of orders of magnitude less than the energy released in the earthquake itself. In many places, the waves reached as far as 2 km (1.2 mi) inland. Because the 1,600 km (1,000 mi) fault affected by the earthquake was in a nearly north–south orientation,

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3968-426: Is only valid for (≤ 7.0). Seismic moment is not a direct measure of energy changes during an earthquake. The relations between seismic moment and the energies involved in an earthquake depend on parameters that have large uncertainties and that may vary between earthquakes. Potential energy is stored in the crust in the form of elastic energy due to built-up stress and gravitational energy . During an earthquake,

4092-785: Is part of the Indo-Australian plate , which underlies the Indian Ocean and Bay of Bengal , and is moving north-east at an average of 60 mm/a (0.075 in/Ms). The India Plate meets the Burma plate (which is considered a portion of the great Eurasian plate ) at the Sunda Trench . At this point, the India Plate subducts beneath the Burma plate, which carries the Nicobar Islands, the Andaman Islands, and northern Sumatra. The India Plate sinks deeper and deeper beneath

4216-463: Is technically difficult since it involves the integration of wave energy over the entire frequency band. To simplify this calculation, he noted that the lowest frequency parts of the spectrum can often be used to estimate the rest of the spectrum. The lowest frequency asymptote of a seismic spectrum is characterized by the seismic moment , M 0  . Using an approximate relation between radiated energy and seismic moment (which assumes stress drop

4340-547: Is the seismic potential for damage ) by the 2004 Indian Ocean earthquake was estimated at 1.1 × 10 joules . The earthquake generated a seismic oscillation of the Earth's surface of up to 200–300 mm (8–12 in), equivalent to the effect of the tidal forces caused by the Sun and Moon. The seismic waves of the earthquake were felt across the planet, as far away as the U.S. state of Oklahoma , where vertical movements of 3 mm (0.12 in) were recorded. By February 2005,

4464-620: Is the same for all earthquakes, one can consider M w   as a measure of the energy E s radiated by earthquakes. Under these assumptions, the following formula, obtained by solving for M 0   the equation defining M w  , allows one to assess the ratio E 1 / E 2 {\displaystyle E_{1}/E_{2}} of energy release (potential or radiated) between two earthquakes of different moment magnitudes, m 1 {\displaystyle m_{1}} and m 2 {\displaystyle m_{2}} : As with

4588-420: Is thus poorly known. It could vary highly from one earthquake to another. Two earthquakes with identical M 0 {\displaystyle M_{0}} but different σ ¯ {\displaystyle {\overline {\sigma }}} would have released different Δ W {\displaystyle \Delta W} . The radiated energy caused by an earthquake

4712-404: The 1960 Chilean and 1964 Alaskan earthquakes. These had M s   magnitudes of 8.5 and 8.4 respectively but were notably more powerful than other M 8 earthquakes; their moment magnitudes were closer to 9.6 and 9.3, respectively. The study of earthquakes is challenging as the source events cannot be observed directly, and it took many years to develop the mathematics for understanding what

4836-426: The 2004 Indian Ocean earthquake and tsunami ). On November 3, 2015, Dutch current affairs television program Zembla reported on a "culture of fear" in the ear, nose and throat department of the UMCU, that would have led to "avoidable" and "serious, deadly complications" endangering the safety of patients. One case was reported in which a patient's carotid artery was accidentally cut during a surgery. The patient died

4960-699: The Boxing Day Tsunami after the Boxing Day holiday, or as the Asian Tsunami , devastated communities along the surrounding coasts of the Indian Ocean, killing an estimated 227,898 people in 14 countries in one of the deadliest natural disasters in recorded history . The direct results caused major disruptions to living conditions and commerce in coastal provinces of surrounded countries, including Aceh (Indonesia), Sri Lanka , Tamil Nadu (India) and Khao Lak (Thailand). Banda Aceh reported

5084-475: The California Institute of Technology estimates that M w  9.2 is best representative of the earthquake's size. More recent studies estimate the magnitude to be M w  9.3. A 2016 study estimated the magnitude to be M w  9.25, while a 2021 study revised its 2007 estimate of M w  9.1 to a new magnitude of M w  9.2. The hypocentre of the main earthquake

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5208-659: The Maldives . Splay faults, or secondary "pop up faults", caused long, narrow parts of the seafloor to pop up in seconds. This quickly elevated the height and increased the speed of waves, destroying the nearby Indonesian town of Lhoknga . Indonesia lies between the Pacific Ring of Fire along the north-eastern islands adjacent to New Guinea , and the Alpide belt that runs along the south and west from Sumatra, Java , Bali , Flores to Timor . The 2002 Sumatra earthquake

5332-437: The local magnitude/Richter scale (M L  ) defined by Charles Francis Richter in 1935, it uses a logarithmic scale ; small earthquakes have approximately the same magnitudes on both scales. Despite the difference, news media often use the term "Richter scale" when referring to the moment magnitude scale. Moment magnitude (M w  ) is considered the authoritative magnitude scale for ranking earthquakes by size. It

5456-569: The subduction zone where the Indian plate slides under (or subducts) the overriding Burma plate. The slip did not happen instantaneously but took place in two phases over several minutes: Seismographic and acoustic data indicate that the first phase involved a rupture about 400 km (250 mi) long and 100 km (60 mi) wide, 30 km (19 mi) beneath the sea bed—the largest rupture ever known to have been caused by an earthquake. The rupture proceeded at about 2.8 km/s (1.74 mi/s; 10,100 km/h; 6,260 mph), beginning off

5580-621: The 1970s, introducing a separate magnitude associated to radiated energy was warranted. Choy and Boatwright defined in 1995 the energy magnitude where E s {\displaystyle E_{\mathrm {s} }} is in J (N·m). Assuming the values of σ̄/μ are the same for all earthquakes, one can consider M w   as a measure of the potential energy change Δ W caused by earthquakes. Similarly, if one assumes η R Δ σ s / 2 μ {\displaystyle \eta _{R}\Delta \sigma _{s}/2\mu }

5704-471: The Burma plate until the increasing temperature and pressure drive volatiles out of the subducting plate. These volatiles rise into the overlying plate, causing partial melting and the formation of magma. The rising magma intrudes into the crust above and exits the Earth's crust through volcanoes in the form of a volcanic arc . The volcanic activity that results as the Indo-Australian plate subducts

5828-426: The Earth on the vertical axis (note the 1 cm scale bar at the bottom for scale). The seismograms are arranged vertically by distance from the epicentre in degrees. The earliest, lower amplitude signal is that of the compressional (P) wave , which takes about 22 minutes to reach the other side of the planet (the antipode ; in this case near Ecuador). The largest amplitude signals are seismic surface waves that reach

5952-518: The Eurasian plate has created the Sunda Arc . As well as the sideways movement between the plates, the 2004 Indian Ocean earthquake resulted in a rise of the seafloor by several metres, displacing an estimated 30 km (7.2 cu mi) of water and triggering devastating tsunami waves. The waves radiated outwards along the entire 1,600 km (1,000 mi) length of the rupture (acting as

6076-530: The Japanese seismologist Kiyoo Wadati showed that the maximum amplitude of an earthquake's seismic waves diminished with distance at a certain rate. Charles F. Richter then worked out how to adjust for epicentral distance (and some other factors) so that the logarithm of the amplitude of the seismograph trace could be used as a measure of "magnitude" that was internally consistent and corresponded roughly with estimates of an earthquake's energy. He established

6200-468: The Pacific Ocean. In comparison to the 2004 Indian Ocean earthquake, the death toll from these earthquakes and tsunamis was significantly lower, primarily because of the lower population density along the coasts near affected areas. Comparisons with earlier earthquakes are difficult, as earthquake strength was not measured systematically until the 1930s. However, historical earthquake strength can sometimes be estimated by examining historical descriptions of

6324-457: The Richter scale, an increase of one step on the logarithmic scale of moment magnitude corresponds to a 10 ≈ 32 times increase in the amount of energy released, and an increase of two steps corresponds to a 10 = 1000 times increase in energy. Thus, an earthquake of M w   of 7.0 contains 1000 times as much energy as one of 5.0 and about 32 times that of 6.0. To make the significance of

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6448-509: The aboriginal tribes escape the tsunami. For example, the folklore of the Onges talks of "huge shaking of ground followed by high wall of water". Almost all of the Onge people seemed to have survived the tsunami. The tsunami devastated the coastline of Aceh province, about 20 minutes after the earthquake. Banda Aceh , the closest major city, suffered severe casualties. The sea receded and exposed

6572-456: The antipode after about 100 minutes. The surface waves can be clearly seen to reinforce near the antipode (with the closest seismic stations in Ecuador), and to subsequently encircle the planet to return to the epicentral region after about 200 minutes. A major aftershock (magnitude 7.1) can be seen at the closest stations starting just after the 200-minute mark. The aftershock would be considered

6696-401: The capital city. The tsunami reached a run-up of 10–20 m (33–66 ft) on the western shorelines of Breueh Island and Nasi Island . Coastal villages were destroyed by the waves. On Weh Island , strong surges were experienced in the port of Sabang , yet there was little damage with reported runup values of 3–5 m (9.8–16.4 ft), most likely due to the island being sheltered from

6820-588: The city was just at the level of the second floor, and there were large amounts of debris piled along the streets and in the ground-floor storefronts. In the seaside section of Ulee Lheue, the flow depths were over 9 m (30 ft). Footage showed evidence of back-flowing of the Aceh River , carrying debris and people from destroyed villages at the coast and transporting them up to 40 km (25 mi) inland. A group of small islands: Weh, Breueh, Nasi, Teunom , Bunta , Lumpat , and Batee lie just north of

6944-467: The coast and appeared like gigantic surfing waves but "taller than the coconut trees and was like a mountain". The second wave was the largest; it came from the west-southwest within five minutes of the first wave. The tsunami stranded cargo ships, barges and destroyed a cement mining facility near the Lampuuk coast, where it reached the fourth level of the building. Meulaboh , a remote coastal city,

7068-590: The coast of Aceh and proceeding north-westerly over about 100 seconds. After a pause of about another 100 seconds, the rupture continued northwards towards the Andaman and Nicobar Islands . The northern rupture occurred more slowly than in the south, at about 2.1 km/s (1.3 mi/s; 7,600 km/h; 4,700 mph), continuing north for another five minutes to a plate boundary where the fault type changes from subduction to strike-slip (the two plates slide past one another in opposite directions). The Indian plate

7192-516: The coastline, rising to 30 m (100 ft) in some areas when travelling inland. Radar satellites recorded the heights of tsunami waves in deep water: the maximum height was at 600 mm (2 ft) two hours after the earthquake, the first such observations ever made. According to Tad Murty , vice-president of the Tsunami Society, the total energy of the tsunami waves was equivalent to about 5 megatons of TNT (21  PJ ), which

7316-508: The damage caused, and the geological records of the areas where they occurred. Some examples of significant historical megathrust earthquakes are the 1868 Arica earthquake in Peru and the 1700 Cascadia earthquake in western North America. The 2004 Indian Ocean earthquake was unusually large in geographical and geological extent. An estimated 1,600 km (1,000 mi) of fault surface slipped (or ruptured) about 15 m (50 ft) along

7440-446: The direct attack by the islands to the south-west. Lhoknga is a small coastal community about 13 km (8.1 mi) south-west of Banda Aceh, located on a flat coastal plain in between two rainforest -covered hills, overlooking a large bay and famous for its large swathe of white sandy beach and surfing activities. The locals reported 10 to 12 waves, with the second and third being the highest and most destructive. Interviews with

7564-461: The direction of 145° east longitude , or perhaps by up to 50 or 60 mm (2.0 or 2.4 in). Because of tidal effects of the Moon, the length of a day increases at an average of 15 microseconds per year, so any rotational change due to the earthquake will be lost quickly. Similarly, the natural Chandler wobble of the Earth, which in some cases can be up to 15 m (50 ft), eventually offset

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7688-463: The distances involved, the tsunami took anywhere from fifteen minutes to seven hours to reach the coastlines. The northern regions of the Indonesian island of Sumatra were hit quickly, while Sri Lanka and the east coast of India were hit roughly 90 minutes to two hours later. Thailand was struck about two hours later despite being closer to the epicentre because the tsunami travelled more slowly in

7812-428: The earthquake (e.g., equation 3 of Venkataraman & Kanamori 2004 ) and μ {\displaystyle \mu } is the average of the shear moduli of the rocks that constitute the fault. Currently, there is no technology to measure absolute stresses at all depths of interest, nor method to estimate it accurately, and σ ¯ {\displaystyle {\overline {\sigma }}}

7936-412: The earthquake's effects were still detectable as a 20 μm (0.02 mm; 0.0008 in) complex harmonic oscillation of the Earth's surface, which gradually diminished and merged with the incessant free oscillation of the Earth more than four months after the earthquake. Because of its enormous energy release and shallow rupture depth, the earthquake generated remarkable seismic ground motions around

8060-399: The earthquake's equivalent double-couple. (More precisely, it is the scalar magnitude of the second-order moment tensor that describes the force components of the double-couple. ) Seismic moment is measured in units of Newton meters (N·m) or Joules , or (in the older CGS system) dyne-centimeters (dyn-cm). The first calculation of an earthquake's seismic moment from its seismic waves

8184-496: The earthquake, its reverberations could still be measured, providing valuable scientific data about the Earth's interior. The 2004 Indian Ocean earthquake came just three days after a magnitude 8.1 earthquake in the sub-antarctic Auckland Islands , an uninhabited region west of New Zealand, and Macquarie Island to Australia's north. This is unusual since earthquakes of magnitude eight or more occur only about once per year on average. The U.S. Geological Survey sees no evidence of

8308-499: The earthquake. The tsunami first struck the eastern coastline and subsequently refracted around the southern point of Sri Lanka ( Dondra Head ). The refracted tsunami waves then inundated the southwestern part of Sri Lanka after some of its energy was reflected from impact with the Maldives. In Sri Lanka, the civilian casualties were second only to those in Indonesia, with approximately 35,000 killed. The eastern shores of Sri Lanka were

8432-409: The energy released, and the stress drop (essentially how much of the potential energy was released). In particular, he derived an equation that relates an earthquake's seismic moment to its physical parameters: with μ being the rigidity (or resistance to moving) of a fault with a surface area of S over an average dislocation (distance) of ū . (Modern formulations replace ūS with

8556-487: The equivalent D̄A , known as the "geometric moment" or "potency". ) By this equation the moment determined from the double couple of the seismic waves can be related to the moment calculated from knowledge of the surface area of fault slippage and the amount of slip. In the case of the Niigata earthquake the dislocation estimated from the seismic moment reasonably approximated the observed dislocation. Seismic moment

8680-460: The fact that they only provided a comparison of the amplitude of waves produced at a standard distance and frequency band; it was difficult to relate these magnitudes to a physical property of the earthquake. Gutenberg and Richter suggested that radiated energy E s could be estimated as (in Joules). Unfortunately, the duration of many very large earthquakes was longer than 20 seconds, the period of

8804-1161: The fault before and after the earthquake (e.g., from equation 1 of Venkataraman & Kanamori 2004 ). These two quantities are far from being constants. For instance, η R {\displaystyle \eta _{R}} depends on rupture speed; it is close to 1 for regular earthquakes but much smaller for slower earthquakes such as tsunami earthquakes and slow earthquakes . Two earthquakes with identical M 0 {\displaystyle M_{0}} but different η R {\displaystyle \eta _{R}} or Δ σ s {\displaystyle \Delta \sigma _{s}} would have radiated different E s {\displaystyle E_{\mathrm {s} }} . Because E s {\displaystyle E_{\mathrm {s} }} and M 0 {\displaystyle M_{0}} are fundamentally independent properties of an earthquake source, and since E s {\displaystyle E_{\mathrm {s} }} can now be computed more directly and robustly than in

8928-501: The first level of a hotel, causing destruction and taking people unaware. Other videos recorded showed that the tsunami appeared like a flood raging inland. The construction of seawalls and breakwaters reduced the power of waves at some locations. The largest run-up measured was at 12.5 m (41 ft) with inundation distance of 390–1,500 m (1,280–4,920 ft) in Yala . In Hambantota , run-ups measured 11 m (36 ft) with

9052-517: The globe, particularly due to huge Rayleigh (surface) elastic waves that exceeded 10 mm (0.4 in) in vertical amplitude everywhere on Earth. The record section plot displays vertical displacements of the Earth's surface recorded by seismometers from the IRIS/USGS Global Seismographic Network plotted with respect to time (since the earthquake initiation) on the horizontal axis, and vertical displacements of

9176-488: The greatest inundation distance of 2 km (1.2 mi). Run-up measurements along the Sri Lankan coasts are at 2.4–4.11 m (7 ft 10 in – 13 ft 6 in). Waves measured on the east coast ranged from 4.5–9 m (15–30 ft) at Pottuvill to Batticaloa at 2.6–5 m (8 ft 6 in – 16 ft 5 in) in the north-east around Trincomalee and 4–5 m (13–16 ft) in

9300-468: The greatest strength of the tsunami waves was in an east–west direction. Bangladesh , which lies at the northern end of the Bay of Bengal , had few casualties despite being a low-lying country relatively near the epicentre. It also benefited from the fact that the earthquake proceeded more slowly in the northern rupture zone, greatly reducing the energy of the water displacements in that region. Coasts that have

9424-461: The hardest hit since it faced the epicentre of the earthquake, while the southwestern shores were hit later, but the death toll was just as severe. The southwestern shores are a hotspot for tourists and fishing. The degradation of the natural environment in Sri Lanka contributed to the high death tolls. Approximately 90,000 buildings and many wooden houses were destroyed. The tsunami arrived on

9548-447: The interactions of forces) this model is called a couple , also simple couple or single couple . If a second couple of equal and opposite magnitude is applied their torques cancel; this is called a double couple . A double couple can be viewed as "equivalent to a pressure and tension acting simultaneously at right angles". The single couple and double couple models are important in seismology because each can be used to derive how

9672-442: The island as a small brown-orange-coloured flood. Moments later, the ocean floor was exposed as much as 1 km (0.62 mi) in places, which was followed by massive second and third waves. Amateur video recorded at the city of Galle showed a large deluge flooding the city, carrying debris and sweeping away people while in the coastal resort town of Beruwala , the tsunami appeared as a huge brown-orange-coloured bore which reached

9796-454: The largest number of deaths. It is the deadliest natural disaster of the 21st century , and the worst tsunami disaster in history. It is also the worst natural disaster in the history of Indonesia, Sri Lanka and Thailand. It was the most powerful earthquake ever recorded in Asia, the most powerful earthquake in the 21st century, and at least the third most powerful earthquake ever recorded in

9920-511: The local magnitude and the surface wave magnitude. Thus, a magnitude zero microearthquake has a seismic moment of approximately 1.1 × 10  N⋅m , while the Great Chilean earthquake of 1960, with an estimated moment magnitude of 9.4–9.6, had a seismic moment between 1.4 × 10  N⋅m and 2.8 × 10  N⋅m . Seismic moment magnitude ( M wg or Das Magnitude Scale ) and moment magnitude ( M w ) scales To understand

10044-416: The locals revealed that the sea temporarily receded and exposed coral reefs . In the distant horizon, gigantic black waves about 30 m (98 ft) high made explosion-like sounds as they broke and approached the shore. The first wave came rapidly landward from the south-west as a turbulent bore about 0.5–2.5 m (1.6–8.2 ft) high. The second and third waves were 15–30 m (49–98 ft) high at

10168-416: The magnitude range 5.0 ≤  M s  ≤ 7.5 is not reliable due to the inconsistency of defined magnitude range (moderate to large earthquakes defined as M s  ≤ 7.0 and M s  = 7–7.5) and scarce data in lower magnitude range (≤ 7.0) which rarely represents the global seismicity (e.g., see Figs. 1A, B, 4 and Table 2 of Percaru and Berckhemer 1978). Furthermore, Equation (1) of Percaru and Berckhemer 1978)

10292-710: The magnitude scales based on M o detailed background of M wg and M w scales is given below. M w scale Hiroo Kanamori defined a magnitude scale (Log W 0  = 1.5 M w  + 11.8, where W 0 is the minimum strain energy) for great earthquakes using Gutenberg Richter Eq. (1). Log Es = 1.5 Ms + 11.8                                                                                     (A) Hiroo Kanamori used W 0 in place of E s (dyn.cm) and consider

10416-427: The magnitude value plausible, the seismic energy released during the earthquake is sometimes compared to the effect of the conventional chemical explosive TNT . The seismic energy E S {\displaystyle E_{\mathrm {S} }} results from the above-mentioned formula according to Gutenberg and Richter to or converted into Hiroshima bombs: For comparison of seismic energy (in joules) with

10540-421: The margins of the continental plates. Despite a delay of up to several hours between the earthquake and the impact of the tsunami, nearly all of the victims were taken by surprise. There were no tsunami warning systems in the Indian Ocean to detect tsunamis or to warn the general population living around the ocean. Tsunami detection is difficult because while a tsunami is in deep water, it has little height and

10664-474: The minor wobble produced by the earthquake. There was 10 m (33 ft) movement laterally and 4–5 m (13–16 ft) vertically along the fault line. Early speculation was that some of the smaller islands south-west of Sumatra, which is on the Burma plate (the southern regions are on the Sunda plate ), might have moved south-west by up to 36 m (120 ft), but more accurate data released more than

10788-674: The minutes preceding a tsunami strike, the sea sometimes recedes temporarily from the coast, which was observed on the eastern earthquake rupture zone such as the coastlines of Aceh, Phuket island, and Khao Lak area in Thailand, Penang island of Malaysia, and the Andaman and Nicobar islands . This rare sight reportedly induced people, especially children, to visit the coast to investigate and collect stranded fish on as much as 2.5 km (1.6 mi) of exposed beach, with fatal results. However, not all tsunamis cause this "disappearing sea" effect. In some cases, there are no warning signs at all:

10912-488: The moment magnitude scale (M ww  , etc.) reflect different ways of estimating the seismic moment. At the beginning of the twentieth century, very little was known about how earthquakes happen, how seismic waves are generated and propagate through the Earth's crust, and what information they carry about the earthquake rupture process; the first magnitude scales were therefore empirical . The initial step in determining earthquake magnitudes empirically came in 1931 when

11036-410: The moment magnitude scale is M w  , with the subscript "w" meaning mechanical work accomplished. The moment magnitude M w   is a dimensionless value defined by Hiroo Kanamori as where M 0   is the seismic moment in dyne ⋅cm (10  N⋅m). The constant values in the equation are chosen to achieve consistency with the magnitude values produced by earlier scales, such as

11160-415: The operating rooms as a result. In December 2016 it was reported that at the UMCU dozens of women who underwent fertility treatment may have had eggs fertilized by sperm cells from someone other than the intended father due to a mix up. Half the women had become pregnant or given birth. 2004 Indian Ocean earthquake On 26 December 2004, at 07:58:53 local time ( UTC+7 ), a major earthquake with

11284-464: The parameters of the source earthquake without having to compensate for the complex ways in which proximity to the coast changes the size and shape of a wave. Before the 2004 quake there were three arguments against a large earthquake occurring in the Sumatra region. After the quake it was considered that earthquake hazard risk would need to be reassessed for regions previously thought to have low risk based on these criteria: The sudden vertical rise of

11408-581: The ratio of seismic Energy ( E ) and Seismic Moment ( M o ), i.e., E / M o  = 5 × 10 , into the Gutenberg–Richter energy magnitude Eq. (A), Hanks and Kanamori provided Eq. (B): Log M0 = 1.5 Ms + 16.1                                                                                   (B) Note that Eq. (B)

11532-463: The region of the original epicentre in the hours and days that followed. The magnitude 8.6 2005 Nias–Simeulue earthquake , which originated off the coast of the Sumatran island of Nias , is not considered an aftershock, despite its proximity to the epicentre, and was most likely triggered by stress changes associated with the 2004 event. The earthquake produced its own aftershocks (some registering

11656-413: The region's north and east coast were Pidie Regency , Samalanga , Panteraja , and Lhokseumawe . The high fatality rate in the area was mainly due to lack of preparation of the community towards a tsunami and limited knowledge and education among the population regarding the natural phenomenon. Helicopter surveys revealed entire settlements virtually destroyed, with destruction extending miles inland. Only

11780-401: The same "line of action" but in opposite directions, will cancel; if they cancel (balance) exactly there will be no net translation, though the object will experience stress, either tension or compression. If the pair of forces are offset, acting along parallel but separate lines of action, the object experiences a rotational force, or torque . In mechanics (the branch of physics concerned with

11904-470: The sea will suddenly swell without retreating, surprising many people and giving them little time to flee. One of the few coastal areas to evacuate ahead of the tsunami was on the Indonesian island of Simeulue , close to the epicentre. Island folklore recounted an earthquake and tsunami in 1907 , and the islanders fled to inland hills after the initial shaking and before the tsunami struck. These tales and oral folklore from previous generations may have helped

12028-502: The seabed around the earthquake zone, which varies in depth between 1,000 and 5,000 m (550 and 2,730 fathoms; 3,300 and 16,400 ft). The survey, conducted using a high-resolution, multi-beam sonar system, revealed that the earthquake had made a considerable impact on the topography of the seabed. 1,500-metre-high (5,000 ft) thrust ridges created by previous geologic activity along the fault had collapsed, generating landslides several kilometres wide. One such landslide consisted of

12152-485: The seabed by several metres during the earthquake displaced massive volumes of water, resulting in a tsunami that struck the coasts of the Indian Ocean. A tsunami that causes damage far away from its source is sometimes called a teletsunami and is much more likely to be produced by the vertical motion of the seabed than by horizontal motion. The tsunami, like all the others, behaved differently in deep water than in shallow water. In deep ocean water, tsunami waves form only

12276-411: The seabed, prompting locals to collect stranded fish and explore the area. Local eyewitnesses described three large waves, with the first wave rising gently to the foundation of the buildings, followed minutes later by a sudden withdrawal of the sea near the port of Ulèë Lheue . This was succeeded by the appearance of two large black-coloured steep waves which then travelled inland into the capital city as

12400-466: The seismic moment calculated from the observed physical dislocation. A double couple model suffices to explain an earthquake's far-field pattern of seismic radiation, but tells us very little about the nature of an earthquake's source mechanism or its physical features. While slippage along a fault was theorized as the cause of earthquakes (other theories included movement of magma, or sudden changes of volume due to phase changes ), observing this at depth

12524-409: The seismic waves from an earthquake can tell about the source event. An early step was to determine how different systems of forces might generate seismic waves equivalent to those observed from earthquakes. The simplest force system is a single force acting on an object. If it has sufficient strength to overcome any resistance it will cause the object to move ("translate"). A pair of forces, acting on

12648-430: The seismic waves generated by an earthquake event should appear in the "far field" (that is, at distance). Once that relation is understood it can be inverted to use the earthquake's observed seismic waves to determine its other characteristics, including fault geometry and seismic moment. In 1923 Hiroshi Nakano showed that certain aspects of seismic waves could be explained in terms of a double couple model. This led to

12772-584: The seismological parameter it is based on, is not measured routinely for smaller quakes. For example, the United States Geological Survey does not use this scale for earthquakes with a magnitude of less than 3.5, which includes the great majority of quakes. Popular press reports most often deal with significant earthquakes larger than M~ 4. For these events, the preferred magnitude is the moment magnitude M w  , not Richter's local magnitude M L  . The symbol for

12896-475: The shallow Andaman Sea off its western coast. The tsunami was noticed as far as Struisbaai in South Africa, about 8,500 km (5,300 mi) away, where a 1.5-metre-high (5 ft) tide surged on shore about 16 hours after the earthquake. It took a relatively long time to reach Struisbaai at the southernmost point of Africa, probably because of the broad continental shelf off South Africa and because

13020-422: The shoreline, houses, except for strongly-built reinforced concrete ones with brick walls, which seemed to have been partially damaged by the earthquake before the tsunami attack, were swept away or destroyed by the tsunami. The area toward the sea was wiped clean of nearly every structure, while closer to the river, dense construction in a commercial district showed the effects of severe flooding. The flow depth at

13144-459: The surface waves used in the measurement of M s  . This meant that giant earthquakes such as the 1960 Chilean earthquake (M 9.5) were only assigned an M s  8.2. Caltech seismologist Hiroo Kanamori recognized this deficiency and took the simple but important step of defining a magnitude based on estimates of radiated energy, M w  , where the "w" stood for work (energy): Kanamori recognized that measurement of radiated energy

13268-446: The survival of the inhabitants. On Maikhao Beach in north Phuket City , Thailand, a 10-year-old British tourist named Tilly Smith had studied tsunamis in geography at school and recognised the warning signs of the receding ocean and frothing bubbles. She and her parents warned others on the beach, which was evacuated safely. John Chroston , a biology teacher from Scotland, also recognised the signs at Kamala Bay north of Phuket, taking

13392-406: The top of the train. Moment magnitude scale The moment magnitude scale ( MMS ; denoted explicitly with M or M w   or Mwg , and generally implied with use of a single M for magnitude ) is a measure of an earthquake 's magnitude ("size" or strength) based on its seismic moment . M w   was defined in a 1979 paper by Thomas C. Hanks and Hiroo Kanamori . Similar to

13516-445: The total energy, the rest being expended in fracturing rock or overcoming friction (generating heat). Nonetheless, seismic moment is regarded as the fundamental measure of earthquake size, representing more directly than other parameters the physical size of an earthquake. As early as 1975 it was considered "one of the most reliably determined instrumental earthquake source parameters". Most earthquake magnitude scales suffered from

13640-431: The tsunami as it was crossing the ocean. These satellites carry radars that measure precisely the height of the water surface; anomalies in the order of 500 mm (20 in) were measured. Measurements from these satellites may prove invaluable for the understanding of the earthquake and tsunami. Unlike data from tide gauges installed on shores, measurements obtained in the middle of the ocean can be used for computing

13764-573: The tsunami would have followed the South African coast from east to west. The tsunami also reached Antarctica, where tidal gauges at Japan's Showa Base recorded oscillations of up to a metre (3 ft 3 in), with disturbances lasting a couple of days. Some of the tsunami's energy escaped into the Pacific Ocean, where it produced small but measurable tsunamis along the western coasts of North and South America, typically around 200 to 400 mm (7.9 to 15.7 in). At Manzanillo , Mexico,

13888-518: The west coast from Moratuwa to Ambalangoda . Sri Lanka tsunami height survey: A regular passenger train operating between Maradana and Matara was derailed and overturned by the tsunami and claimed at least 1,700 lives, the largest single rail disaster death toll in history. Estimates based on the state of the shoreline and a high-water mark on a nearby building place the tsunami 7.5–9 m (25–30 ft) above sea level and 2–3 m (6 ft 7 in – 9 ft 10 in) higher than

14012-405: The world since modern seismography began in 1900. It had the longest fault rupture ever observed, between 1,200 km and 1,300 km (720 mi and 780 mi), and had the longest duration of faulting ever observed, at least ten minutes. It caused the planet to vibrate as much as 10 mm (0.4 in), and also remotely triggered earthquakes as far away as Alaska . Its epicentre

14136-400: Was already derived by Hiroo Kanamori and termed it as M w . Eq. (B) was based on large earthquakes; hence, in order to validate Eq. (B) for intermediate and smaller earthquakes, Hanks and Kanamori (1979) compared this Eq. (B) with Eq. (1) of Percaru and Berckhemer (1978) for the magnitude 5.0 ≤  M s  ≤ 7.5 (Hanks and Kanamori 1979). Note that Eq. (1) of Percaru and Berckhemer (1978) for

14260-471: Was among the hardest hit by the tsunami. The waves arrived after the sea receded about 500 m (1,600 ft), followed by an advancing small tsunami. The second and third destructive waves arrived later, which exceeded the height of the coconut trees. The inundation distance is about 5 km (3.1 mi). Other towns on Aceh's west coast hit by the disaster included Leupung , Lhokruet , Lamno , Patek, Calang , and Teunom . Affected or destroyed towns on

14384-536: Was approximately 160 km (100 mi) off the western coast of northern Sumatra, in the Indian Ocean just north of Simeulue island at a depth of 30 km (19 mi) below mean sea level (initially reported as 10 km or 6.2 mi). The northern section of the Sunda megathrust ruptured over a length of 1,300 km (810 mi). The earthquake (followed by the tsunami) was felt in Bangladesh , India , Malaysia , Myanmar , Thailand , Sri Lanka and

14508-422: Was between Simeulue and mainland Sumatra. The plight of the affected people and countries prompted a worldwide humanitarian response , with donations totalling more than US$ 14 billion (equivalent to US$ 23 billion in 2023 currency). The 2004 Indian Ocean earthquake was initially documented as having a moment magnitude of 8.8. The United States Geological Survey has its estimate of 9.1. Hiroo Kanamori of

14632-451: Was by Keiiti Aki for the 1964 Niigata earthquake . He did this two ways. First, he used data from distant stations of the WWSSN to analyze long-period (200 second) seismic waves (wavelength of about 1,000 kilometers) to determine the magnitude of the earthquake's equivalent double couple. Second, he drew upon the work of Burridge and Knopoff on dislocation to determine the amount of slip,

14756-418: Was caused by the 1883 eruption of Krakatoa . Not every earthquake produces large tsunamis: on 28 March 2005, a magnitude 8.7 earthquake hit roughly the same area of the Indian Ocean but did not result in a major tsunami. The first warning sign of a possible tsunami is the earthquake itself. However, tsunamis can strike thousands of kilometres away where the earthquake is felt only weakly or not at all. Also, in

14880-823: Was due to the 2004 Indian Ocean earthquake. This quake, together with the Great Alaskan earthquake (1964) and the Great Chilean earthquake (1960), account for almost half of the total moment. Since 1900, the only earthquakes recorded with a greater magnitude were the 1960 Valdivia earthquake (magnitude 9.5) and the 1964 Alaska earthquake in Prince William Sound (magnitude 9.2). The only other recorded earthquakes of magnitude 9.0 or greater were off Kamchatka , Russia, on 5 November 1952 (magnitude 9.0) and Tōhoku, Japan (magnitude 9.1) in March 2011 . Each of these megathrust earthquakes also spawned tsunamis in

15004-420: Was extreme on the northwestern areas of the city, immediately inland of the aquaculture ponds, and directly facing the Indian Ocean. The tsunami height was reduced from 12 m (39 ft) at Ulee Lheue to 6 m (20 ft) a further 8 km (5.0 mi) to the north-east. The inundation was observed to extend 3–4 km (1.9–2.5 mi) inland throughout the city. Within 2–3 km (1.2–1.9 mi) of

15128-580: Was not possible, and understanding what could be learned about the source mechanism from the seismic waves requires an understanding of the source mechanism. Modeling the physical process by which an earthquake generates seismic waves required much theoretical development of dislocation theory , first formulated by the Italian Vito Volterra in 1907, with further developments by E. H. Love in 1927. More generally applied to problems of stress in materials, an extension by F. Nabarro in 1951

15252-593: Was recognized by the Russian geophysicist A. V. Vvedenskaya as applicable to earthquake faulting. In a series of papers starting in 1956 she and other colleagues used dislocation theory to determine part of an earthquake's focal mechanism, and to show that a dislocation – a rupture accompanied by slipping – was indeed equivalent to a double couple. In a pair of papers in 1958, J. A. Steketee worked out how to relate dislocation theory to geophysical features. Numerous other researchers worked out other details, culminating in

15376-521: Was very similar to a relationship between M L   and M 0   that was reported by Thatcher & Hanks (1973) Hanks & Kanamori (1979) combined their work to define a new magnitude scale based on estimates of seismic moment where M 0 {\displaystyle M_{0}} is defined in newton meters (N·m). Moment magnitude is now the most common measure of earthquake size for medium to large earthquake magnitudes, but in practice, seismic moment (M 0  ),

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