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Query: What was the largest seismic event in recorded history?
The 1960 Valdivia earthquake (Spanish: Terremoto de Valdivia) or Great Chilean earthquake (Gran terremoto de Chile) of 22 May is the most powerful earthquake ever recorded. Various studies have placed it at 9.4–9.6 on the moment magnitude scale. It occurred in the afternoon (19:11 GMT, 15:11 local time), and lasted approximately 10 minutes. The resulting tsunami affected southern Chile, Hawaii, Japan, the Philippines, eastern New Zealand, southeast Australia and the Aleutian Islands.
Large-scale fossil fuel extraction can generate earthquakes. Induced seismicity can be also related to underground gas storage operations. The 2013 September–October seismic sequence occurred 21 km off the coast of the Valencia Gulf (Spain) is probably the most known case of induced seismicity related to Underground Gas Storage operations (the Castor Project). In September 2013, after the injection operations started, the Spanish seismic network recorded a sudden increase of seismicity. More than 1,000 events with magnitudes () between 0.7 and 4.3 (the largest earthquake ever associated with gas storage operations) and located close the injection platform were recorded in about 40 days. Due to the significant population concern the Spanish Government halted the operations. By the end of 2014, the Spanish government definitively terminated the concession of the UGS plant. Since January 2015 about 20 people who took part in the transaction and approval of the Castor Project were indicted.
Seismic risk refers to the risk of damage from earthquake to a building, system, or other entity. Seismic risk has been defined, for most management purposes, as the potential economic, social and environmental consequences of hazardous events that may occur in a specified period of time. A building located in a region of high seismic hazard is at lower risk if it is built to sound seismic engineering principles. On the other hand, a building located in a region with a history of minor seismicity, in a brick building located on fill subject to liquifaction can be as high or higher risk.
The sharp seismicity increase observed in recent years in the Western Canada Sedimentary Basin is inferred to be triggered by hydraulic fracturing operations. Most of the seismic events reported in this period are closely located to hydraulic fracturing wells completed in western Alberta and northeast British Columbia. In response to this increased seismicity, in 2015 the Alberta Energy Regulator released the Subsurface Order No. 2 that requires mandatory implementation of a Traffic-Light Protocol (TLP) based on the local magnitude (M) of seismic events detected during the monitored operations. According to this TLP, the hydraulic fracturing operations can continue as planned when the Mof the detected seismic events are below 2.0 (green light), must be modified and reported to the regulator when a seismic event of M between 2.0 and 4.0 is detected (amber light), and must be immediately ceased when a seismic event of M > 4.0 is detected within 5 km of a hydraulic fracturing well (red light). The BC Oil and Gas Commissionimplemented a similar TLP where the seismicity and surface ground motions must be adequately monitored during hydraulic fracturing operations, and must be suspended if a M > 4 is detected within 3 km from the well. M > 4 has been chosen as a red-light threshold by both jurisdictions in western Canada (Alberta and British Columbia) as a seismic event with magnitude below 4 corresponds to a minor earthquake that may be lightly felt, but with no expected property damage.  The following table lists some amber or red-light TLP seismic events reported in the Horn River Basin in northeast BC, and in Fox Creek, Alberta. The increased seismic activity in these two areas have been closely attributed to hydraulic fracturing operations.
Although The Volcano is estimated to have last erupted 150 years ago, it is one of the five volcanoes in the Northern Cordilleran Volcanic Province that have recorded seismicity since 1985. Others include Castle Rock (two events), Hoodoo Mountain (eight events), Crow Lagoon (four events) and the Mount Edziza volcanic complex (eight events). Seismic data suggest that these volcanoes still contain active magma chambers, indicating that some Northern Cordilleran volcanoes are probably active, with significant potential hazards. The seismic activity corresponds both with some of Canada's recently formed volcanoes and with persistent volcanoes that have had major explosive activity throughout their history, such as Hoodoo Mountain and the Mount Edziza volcanic complex.
The largest event prompted concern from local residents. The six borehole seismometers installed near the Basel injection well to monitor the natural background seismicity and the geothermal stimulation recorded more than 13,500 potential events connected with the geothermal project, from which 3,124 were of sufficient quality to permit [hypocenter] determinations in the period 2–12 December 2006, which spanned the main stimulation and the decline in the event rate. During the post-stimulation period from 13 December 2006 onward, a further 350 locatable events were detected up to 2 May 2007, by which time events were occurring sporadically at around one per day. In all, locations for more than 3,500 events were determined.
Magnitude scales generally are based on instrumental measurement of some aspect of the seismic wave as recorded on a seismogram. Where such records do not exist, magnitudes can be estimated from reports of the macroseismic events such as described by intensity scales.
Significant earthquakes centred on Dalton/Gunning include an ML5.3 event on 5 July 1888 that was felt in Sydney and represents the first record of seismic activity in the area; the largest recorded event - an ML5.6 event on 18 November 1934 that was also felt in Sydney and agitated the water in the Manuka Pool in Canberra; an ML5.5 event on 10–11 March 1949 that caused minor cracking in Canberra buildings; and the ML4.3 Oolong event on 9 August 1984 which damaged Oolong Homestead and the Anglican Church.
Merapi erupted three times on Monday afternoon spewing lava down its southern and south-eastern slopes. Three major eruptions were recorded at 14:04, 14:24 and 15:15 local time. On this day, 222 volcanic seismic events and 454 avalanche seismic events were recorded by Center for Volcanology and Geological Hazard Mitigation monitoring staff at Merapi.
In all, between December 2006 and March 2007, the six borehole seismometers installed near the Basel injection well recorded more than 13,500 potential events connected with the geothermal project. The 200 largest were between magnitudes 0.7 and 3.4. Nine of these events had an of 2.5 or larger. The remainder were too small to be observed or felt at the surface. Between December 2 and January 24, 168 seismic events with magnitude greater than 0.6 occurred within 1 km of the wellbore, at depths of 4–5 km, near the well bottom.
The slip caused by this earthquake can be divided into 'coseismic' slip that occurred immediately before, during and immediately after the event, and a long period of slow post-seismic slip that continued for more than a year after the original event. The slow post-seismic slip following this earthquake had a large seismic moment compared with the coseismic slip associated with the main event. The post-seismic slip occurred in two phases; an initial faster short-term phase that lasted for about ten days, terminating with the largest aftershock, followed by a long-term slower phase. The slip area of the initial phase matches the rupture area for the main event. The second phase migrated significantly further down-dip and to the south, along the plate boundary.
The filling (impounding) of reservoirs has often been attributed to reservoir-triggered seismicity (RTS) as seismic events have occurred near large dams or within their reservoirs in the past. These events may have been triggered by the filling or operation of the reservoir and are on a small scale when compared to the amount of reservoirs worldwide. Of over 100 recorded events, some early examples include the tall Marathon Dam in Greece (1929), the tall Hoover Dam in the U.S. (1935). Most events involve large dams and small amounts of seismicity. The only four recorded events above a 6.0-magnitude (M) are the tall Koyna Dam in India and the Kremasta Dam in Greece which both registered 6.3-M, the high Kariba Dam in Zambia at 6.25-M and the Xinfengjiang Dam in China at 6.1-M. Disputes have occurred regarding when RTS has occurred due to a lack of hydrogeological knowledge at the time of the event. It is accepted, though, that the infiltration of water into pores and the weight of the reservoir do contribute to RTS patterns. For RTS to occur, there must be a seismic structure near the dam or its reservoir and the seismic structure must be close to failure. Additionally, water must be able to infiltrate the deep rock stratum as the weight of a deep reservoir will have little impact when compared the deadweight of rock on a crustal stress field, which may be located at a depth of or more.
The EAR is the largest seismically active rift system on Earth today. The majority of earthquakes occur near the Afar Depression, with the largest earthquakes typically occurring along or near major border faults. Seismic events in the past century are estimated to have reached a maximum moment magnitude of 7.0. The seismicity trends parallel to the rift system, with a shallow focal depth of beneath the rift axis. Further away from the rift axis, focal depths can reach depths of over . Focal mechanism solutions strike NE and frequently demonstrate normal dip-slip faults, although left-lateral motion is also observed.
In the context of seismic migration, specularity is defined as the cosine of the angle made by the surface normal vector and the angle bisector of the angle defined by the directions of the incident and diffracted rays. For a purely specular seismic event the value of specularity should be equal to unity, as the angle between the surface normal vector and the angle bisector should be zero, according to Snell's Law. For a diffractive seismic event, the specularity can be sub-unitary. During the seismic migration, one can filter each seismic event according to the value of specularity, in order to enhance the contribution of diffractions in the seismic image. Alternatively, the events can be separated in different sub-images according to the value of specularity to produce a specularity gather.
Information on the timing and magnitude of seismic events that occurred before instrumental recording can be obtained from excavations across faults that are thought to be seismically active and by studying recent sedimentary sequences for evidence of seismic activity such as seismites or tsunami deposits.
Prior to the 1989 Loma Prieta earthquake, that segment of the San Andreas fault system recorded much less seismic activity than other parts of the fault. The main shock and aftershocks of the 1989 event occurred within the previous seismic gap.
The Gathering 2009 was a two-day weekend event, celebrating Scottish culture, held between 25–26 July 2009, as part of Homecoming 2009. The event was held at Holyrood Park, Scotland, and attracted around 47,000 people from all over the world. Over 125 Scottish clans were represented in what was described as the largest Highland Games in Scotland's history. A clan convention also took place, also the largest recorded meeting of chiefs.
The area is the most seismically active in Argentina. This seismic event was the largest in 20 years; the 1985 Mendoza earthquake (magnitude 6.0) caused 6 casualties and thousands of damaged houses and was centered at Godoy Cruz, just 4 km at south of Mendoza.
More than a million earthquakes are recorded each year, by a worldwide system of earthquake detection stations. The propagation velocity of the seismic waves depends on density and elasticity of the earth materials. In other words, the speeds of the seismic waves vary as they travel through different materials in the earth. The two main components of a seismic event are body waves and surface waves. Both of these have different modes of wave propagation.
The eruptions on Tuesday started at 17:02. By 18:54 pyroclastic activity had begun to subside following 12 eruption-associated events being recorded by CVGHM monitors. 232 volcanic seismic events, 269 avalanche seismic events, 4 lava flow seismic events and 6 pyroclastic flows were recorded in the 24 hours of 26 October. The eruptive events were classified as "explosive events" with volcanic bursts of ejected material, visible flame and pyroclastic hot air flows. A column of smoke rose from the top to a vertical distance of from the summit of Mount Merapi. The first fatalities occurred on this day.
A mine explosion was unlikely, as it was 170 times more powerful than the largest mining explosion known in Australia up to that time. The Urban Geoscience Division of the Australian Geological Survey Organisation determined that the seismic traces of the event "showed similar characteristics consistent with typical seismic activity for Western Australia," and that the event was most likely an earthquake.
Seismic migration is the process by which seismic events are geometrically re-located in either space or time to the location the event occurred in the subsurface rather than the location that it was recorded at the surface, thereby creating a more accurate image of the subsurface.
Between 1970 and 2005 more than 20 small earthquakes were recorded at the volcano. The magnitudes of these events were generally no higher than 2.0 on the Richter magnitude scale and they originated to less than below the surface. Other volcanoes in the with recorded seismicity include Mount Garibaldi, Mount Cayley massif and . Seismic data suggest that these volcanoes still contain active magma chambers, indicating that some Garibaldi Belt volcanoes are probably active with significant potential hazards. The seismic activity corresponds with some of Canada's recently formed volcanoes and with persistent volcanoes that have had major explosive activity throughout their history such as Mount Garibaldi and the Mount Cayley and Mount Meager massifs.
The low-level seismic activity documented on Lōihi since 1959 has shown that between two and ten earthquakes per month are traceable to the summit. Earthquake swarm data have been used to analyze how well Lōihi's rocks propagate seismic waves and to investigate the relationship between earthquakes and eruptions. This low level activity is periodically punctuated by large swarms of earthquakes, each swarm comprising up to hundreds of earthquakes. The majority of the earthquakes are not distributed close to the summit, though they follow a north–south trend. Rather, most of the earthquakes occur in the southwest portion of Lōʻihi. The largest recorded swarms took place on Lōihi in 1971, 1972, 1975, 1991–92 and 1996. The nearest seismic station is around from Lōʻihi, on the south coast of Hawaii. Seismic events that have a magnitude under 2 are recorded often, but their location cannot be determined precisely as it can for larger events. In fact, HUGO (Hawaii Undersea Geological Observatory), positioned on Lōihi's flank, detected ten times as many earthquakes as were recorded by the Hawaiian Volcano Observatory (HVO) seismic network.
Before this seismic event there was an unusual increase in seismic activity (seismic swarm) that began on Saturday, April 22 and before the event of magnitude 6.9 more than 180 earthquakes (precursor earthquakes) had been recorded, being one of the most strong that of magnitude 6.0 of the dawn of the April 22, 2017.