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70 BC Shandong earthquake
The 70 BC Shandong earthquake struck eastern China on 1 June 70 BC during the Han Dynasty, destroying 49 shires and killing more than 6,000 people.
744 Shimabara earthquake
The 744 Shimabara earthquake, also known as the 744 Higo earthquake, struck Higo Province on Japan's Kyushu island, sweeping away more than 1,520 people and causing over 280 landslides.
8.2 kiloyear event
The 8.2 kiloyear event was an abrupt cooling of the Northern Hemisphere about 8,200 years ago, triggered when the drainage of glacial Lake Agassiz-Ojibway slowed the Atlantic overturning circulation.
838 Uzbekistan earthquake
The 838 Uzbekistan earthquake was a destructive earthquake that struck the Fergana region of Central Asia in 838 AD, recorded with about 15,000 deaths and extreme damage, the earliest listed for the Fergana depression.
844 Antakya earthquake
The 844 Antakya earthquake was a historical Abbasid-era earthquake, dated to 18 September 844 by modern catalogs, that Arabic chronicles say destroyed Antioch and shook Damascus, al-Jazirah, and Mosul.
845 Al-Mawsil earthquake
The 845 Al-Mawsil earthquake was a destructive earthquake reported at Mosul (Al-Mawsil) in northern Iraq in the mid-ninth century, claimed in Arabic chronicles to have killed 50,000 people.
850 Rey (Ray) earthquake
The 850 Rey (Ray) earthquake was a destructive historical earthquake that struck the city of Rey, near present-day Tehran, Iran, in 850, with a recorded death toll of 45,000.
856 Damghan earthquake
The 856 Damghan earthquake, also called the Qumis earthquake, struck northeastern Iran on 22 December 856 with an estimated magnitude of 7.9, killing more than 200,000 people.
856 Tunisia earthquake
The 856 Tunisia earthquake struck Tunis in December 856, destroying many houses and reportedly killing 45,000 inhabitants, and remains the largest reported historical earthquake of the Tunis area.
871 Saimareh earthquake
The 871 Saimareh earthquake was a destructive earthquake in the Zagros region of western Iran, cataloged at magnitude 6.8 with about 20,000 deaths, possibly triggering the Simareh landslide.
885 Egypt earthquake
The 885 Egypt earthquake was a destructive shock that struck Lower Egypt in November 885, reportedly killing about 1,000 people and damaging the mosque of 'Amr at Fustat.
887 Niigata earthquake
The 887 Niigata earthquake, known in Japanese as the Ninna earthquake, was a great Nankai Trough earthquake off southwest Japan in August 887, with an estimated magnitude of 8.3.
893 Armenia earthquake
The 893 Armenia earthquake struck Dvin, then a capital and religious center of medieval Armenia, on the evening of 28 December 893, with death tolls estimated from 20,000 to 150,000.
943 Turkmenistan earthquake
The 943 Turkmenistan earthquake was a medieval earthquake that destroyed the city of Nisa in August 943, killing more than 5,000 people, one of the earliest recorded in the Kopet Dag region.
946 eruption of Mount Paektu
The 946 eruption of Mount Paektu, also called the Millennium Eruption, was a large eruption of the Changbaishan volcano on the North Korea–China border in late 946.
978 Taheri (Siraf) earthquake
The 978 Siraf earthquake struck the port city of Siraf, near present Taheri in Bushehr Province, Iran, on 17 June 978, damaging most of its houses and contributing to the port's decline.
A23a
A23a, also known as Iceberg A23a, is a giant tabular iceberg that calved from Antarctica's Filchner Ice Shelf in 1986 and drifted to South Georgia.
Abiogenic petroleum origin
Abiogenic petroleum origin, also called abiotic oil, is the hypothesis that oil and gas form from inorganic carbon deep in the Earth, a theory lacking scientific support.
Abyssal zone
The abyssal zone, also called the abyssopelagic zone, is the deep-ocean zone at depths of roughly 3,000 to 6,000 meters, where temperatures stay near freezing and no sunlight reaches.
Accelerated erosion
Accelerated erosion is soil erosion occurring faster than the normal geologic rate for a site, usually because human activities such as tillage, grazing, and timber cutting remove protective vegetation.
Accelerometry
Accelerometry is the measurement of acceleration over time using accelerometers, typically in g or m/s² on one to three axes, underpinning strong-motion seismology, structural health monitoring, and animal biologging.
Accretionary wedge
An accretionary wedge, also called an accretionary prism, is a body of sediment scraped off a subducting tectonic plate and thrust onto the overriding plate at a convergent boundary.
Accumulated cyclone energy
Accumulated cyclone energy (ACE) is an index measuring tropical cyclone and seasonal activity by summing squared sustained wind speeds, used by NOAA to classify hurricane seasons.
Accumulation zone
The accumulation zone is the higher part of a glacier where annual accumulation from snowfall, wind drift, and avalanches exceeds ablation, separated from the ablation zone by the equilibrium line.
Acid neutralizing capacity
Acid neutralizing capacity (ANC) is a measure of the ability of water or soil to neutralize added acids, serving as the standard indicator of surface water sensitivity to acidification.
Acid rain
Acid rain, also called acid deposition, is rain, snow, fog, or dry particles made acidic by sulfur dioxide and nitrogen oxides from fossil fuel combustion.
Acid sulfate soil
Acid sulfate soil is a soil or sediment containing iron sulfides, most commonly pyrite; when drained or excavated, these oxidize to sulfuric acid, harming waterways, ecosystems, and infrastructure.
Acoustic Doppler current profiler
An acoustic Doppler current profiler (ADCP) is a sonar instrument that measures current speed and direction at many depths by analyzing the Doppler shift of sound echoes.
Acoustic Doppler velocimetry
Acoustic Doppler velocimetry is a technique that measures fluid velocity from the Doppler shift of sound echoed by particles moving with the flow, used in turbulence and current studies.
Acoustic imaging
Acoustic imaging forms images of underwater objects and environments from sound-wave echoes, and it is the dominant technique for mapping the seafloor and inspecting submerged structures.