Earthquake in the context of "Seismometer"

The Minoan eruption was a catastrophic volcanic eruption that devastated the Aegean island of Thera (also called Santorini) circa 1600 BC. It destroyed the Minoan settlement at Akrotiri, as well as communities and agricultural areas on nearby islands and the coast of Crete with subsequent earthquakes and tsunamis. With a Volcanic Explosivity Index (VEI) of 7, it resulted in the ejection of approximately 28–41 km (6.7–9.8 cu mi) of dense-rock equivalent (DRE), the eruption was one of the largest volcanic events in human history. Because tephra from the Minoan eruption serves as a marker horizon in nearly all archaeological sites in the Eastern Mediterranean, its precise date is of high importance and has been fiercely debated among archaeologists and volcanologists for decades, without coming to a definite conclusion.

Although there are no clear ancient records of the eruption, its plume and volcanic lightning may have been described in the Egyptian Tempest Stele. The Chinese Bamboo Annals reported unusual yellow skies and summer frost at the beginning of the Shang dynasty, which may have been a consequence of volcanic winter (similar to 1816, the Year Without a Summer, after the 1815 eruption of Mount Tambora).

A natural phenomenon is an observable event which is not man-made. Examples include: sunrise, weather, fog, thunder, tornadoes; biological processes, decomposition, germination; physical processes, wave propagation, erosion; tidal flow, and natural disasters such as electromagnetic pulses, volcanic eruptions, hurricanes and earthquakes.

Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle along the subduction zone. They are the principal way by which continental growth is achieved.

Island arcs can either be active or inactive based on their seismicity and presence of volcanoes. Active arcs are ridges of recent volcanoes with an associated deep seismic zone. They also possess a distinct curved form, a chain of active or recently extinct volcanoes, a deep-sea trench, and a large negative Bouguer anomaly on the convex side of the volcanic arc. The small positive gravity anomaly associated with volcanic arcs has been interpreted by many authors as due to the presence of dense volcanic rocks beneath the arc. Inactive arcs are a chain of islands which contains older volcanic and volcaniclastic rocks.

A natural disaster is the very harmful impact on a society or community brought by natural phenomenon or hazard. Some examples of natural hazards include avalanches, droughts, earthquakes, floods, heat waves, landslides - including submarine landslides, tropical cyclones, volcanic activity and wildfires. Additional natural hazards include blizzards, dust storms, firestorms, hails, ice storms, sinkholes, thunderstorms, tornadoes and tsunamis.

A natural disaster can cause loss of life or damage property. It typically causes economic damage. How bad the damage is depends on how well people are prepared for disasters and how strong the buildings, roads, and other structures are.

A qanāt (Persian: قَنَات) or kārīz (کَارِیز) is a water supply system that was developed in ancient Iran for the purpose of transporting usable water to the surface from an aquifer or a well through an underground aqueduct. Originating approximately 3,000 years ago, its function is essentially the same across the Middle East and North Africa, but it is known by a variety of regional names beyond today's Iran, including: kārēz in Afghanistan and Pakistan; foggāra in Algeria; khettāra in Algeria and Morocco; the daoudi-type falaj in Oman and the United Arab Emirates; and ʿuyūn in Saudi Arabia. In addition to those in Iran, the largest extant and functional qanats are located in Afghanistan, Xinjiang in China (the Turpan water system), Oman, and Pakistan.

Proving crucial to water supply in areas with hot and dry climates, a qanat enables water to be transported over long distances by largely eliminating the risk of much of it evaporating on the journey. The system also has the advantage of being fairly resistant to natural disasters, such as floods and earthquakes, as well as to man-made disasters, such as wartime destruction and water supply terrorism. Furthermore, it is almost insensitive to varying levels of precipitation, delivering a flow with only gradual variations from wet to dry years.

Seismic magnitude scales are used to describe the overall strength or "size" of an earthquake. These are distinguished from seismic intensity scales that categorize the intensity or severity of ground shaking (quaking) caused by an earthquake at a given location. Magnitudes are usually determined from measurements of an earthquake's seismic waves as recorded on a seismogram. Magnitude scales vary based on what aspect of the seismic waves are measured and how they are measured. Different magnitude scales are necessary because of differences in earthquakes, the information available, and the purposes for which the magnitudes are used.