Glossary

Academia Sinica

Taiwan’s national academic institution, founded in 1928, with 24 institutes and 9 research centres in three divisions: mathematics and physical sciences, life sciences, and humanities and social sciences. Its main campus is in Nankang (Nangang), one of Taipei’s 12 districts. Read more →

ASIAA Academia Sinica Institute of Astronomy and Astrophysics

Academia Sinica’s astronomy institute, a preparatory office from 1993 and a full institute since June 2010. It is based on the National Taiwan University campus and takes part in projects such as ALMA, the Submillimeter Array and the Greenland Telescope. Read more →

Chi-Chi earthquake 1999

The earthquake of 21 September 1999 (1:47 a.m. local time) in Nantou County, central Taiwan, when the Chelungpu thrust fault ruptured along about 100 kilometres: moment magnitude 7.6 according to the USGS, 7.3 on the local scale. A preliminary count gave 2,333 dead; it also damaged high-rise buildings in the Taipei Basin and shaped Taiwan’s later monitoring and early warning. Read more →

CWA Central Weather Administration

Taiwan’s agency for meteorological and seismological operations, under the Ministry of Transportation and Communications. Founded in 1941 as the Central Weather Bureau, it took its present name on 15 September 2023. Its Weather Forecast Center issues typhoon warnings and its Seismological Center, established on 1 July 1989, reports earthquakes and issues tsunami warnings. Read more →

Earthquake early warning EEW

A system that detects an earthquake that has already begun and sends an alert before the slower, damaging waves reach places further away; it does not predict earthquakes. The CWA launched its service in 2013 and has sent alerts to phones since 2016, with about 20 seconds of warning on average; close to the epicentre lies a blind zone that cannot be warned in time. Read more →

Epicentre and hypocentre

The hypocentre (or focus) is the point inside the Earth where an earthquake rupture begins; the epicentre is the point on the surface directly above it. Earthquake reports give the epicentre together with the depth of the hypocentre. Read more →

Fault

A fracture or zone of fractures between two blocks of rock along which the blocks have moved. An earthquake happens when the rock on one side of a fault suddenly slips relative to the other. Read more →

GNSS Global Navigation Satellite System

The generic term for satellite navigation systems with global coverage, such as GPS, GLONASS, Galileo and BeiDou. Fixed GNSS stations measure their position so precisely that they show how the ground moves by millimetres a year; the CWA began its GPS network for crustal movement in 1993. Read more →

Institute of Earth Sciences IES, Academia Sinica

Academia Sinica’s institute for geophysics and geochemistry, which grew out of a seismic studies group: a preparatory office in 1976, a full institute since August 1982. It is particularly strong in seismology and runs geophysical and geodetic networks on Taiwan alongside those of the CWA. Read more →

Magnitude

A number describing the size of an earthquake itself, the same for every place where it is felt. The scale is logarithmic: one whole unit means ten times the amplitude on a seismogram and about 32 times more energy. Different scales can give different values for one earthquake, for example 7.3 (local scale) and 7.6 (moment magnitude) for Chi-Chi in 1999. Read more →

Natural frequency

The rate at which a structure prefers to sway once set in motion, measured in hertz (Hz, one cycle per second). Seismometers inside Taipei 101 show that its fundamental mode is near 0.15 Hz, so one full sway takes about six to seven seconds; the damper is tuned to that rhythm. Read more →

Normal fault

A fault on which the block above the fault plane moves down relative to the block below, typically where the crust is being pulled apart. The Shanchiao fault on the western edge of the Taipei Basin is a normal fault. Read more →

NSTC National Science and Technology Council

The Executive Yuan’s decision-making body for science and technology, formed in 2022 from the Ministry of Science and Technology. Its missions are science and technology policy, support for basic research, science parks, and innovation and entrepreneurship. Read more →

NTU National Taiwan University

A university in Taipei that traces its history to Taihoku Imperial University, founded in 1928, and has had its present name since 1945. Its main campus is on Roosevelt Road and also houses Academia Sinica’s astronomy institute. Read more →

Plate tectonics

The theory that the Earth’s outer shell is broken into plates that move slowly against one another; most large earthquakes happen where plates meet. Taiwan lies where the Philippine Sea plate converges with the edge of the Eurasian plate, at about 8 centimetres a year. Read more →

Seismic intensity

How strongly the ground shakes at a particular place, so one earthquake has different intensities in different towns. The Central Weather Administration’s scale is based on measured ground motion; its top level, 7, was set in 2000 at an acceleration of 400 gal or more (1 gal = 1 cm/s²), and since 2020 levels 5 and 6 are split into “weak” and “strong”. Read more →

Seismometer seismograph, seismogram

An instrument that senses ground motion; a seismograph records it, and the record is a seismogram. Taiwan’s first seismograph, a Gray-Milne instrument, arrived in Taipei on 19 December 1897; since 2008 the CWA has also placed seismometers in boreholes about 300 metres deep, away from surface noise. Read more →

Shanchiao fault

A normal fault running north–south along the western edge of the Taipei Basin. Boreholes show repeated sudden subsidence roughly 11,000, 9,000–9,300 and 8,400–8,600 years ago, in earthquakes estimated at about magnitude 6.9 to 7.1; researchers count it among the major seismic hazards for metropolitan Taipei. Read more →

Strong-motion station

A station with an instrument that records the acceleration of the ground during strong shaking near an earthquake. From 1991 Taiwan’s strong-motion programme set up 689 free-field stations; their records, including more than 30,000 from the 1999 Chi-Chi earthquake and its aftershocks, are key inputs for seismic design codes. Read more →

Subduction zone

A boundary where one tectonic plate slides beneath another and sinks into the mantle. Taiwan lies between two subduction zones dipping in opposite directions: the Manila Trench to the south and the Ryukyu Trench to the north-east. Read more →

Taipei 101

A 508-metre, 101-storey tower in Taipei’s Xinyi district, completed in 2004. Its shape was refined to reduce wind forces in a typhoon-prone city, and it carries a tuned mass damper that visitors to the 89th-floor observation deck can see. Read more →

Taipei Basin

The lowland in northern Taiwan where most of Taipei lies, formed by fault displacement and shaped by the Danshui (Tamsui), Xindian and Keelung Rivers. It is filled with river sediments that thicken towards the north-west, and this soft ground affects how the city shakes in large earthquakes. Read more →

Tatun Volcano Group Datun

The volcanic hills on Taipei’s northern edge, most of which lie within Yangmingshan National Park. They are watched by the Taiwan Volcano Observatory-Tatun, founded on 17 October 2011, which monitors volcanic seismicity and works with Academia Sinica’s Institute of Earth Sciences. Read more →

Thrust fault

A reverse fault with a shallow dip: the upper block is pushed up and over the lower one, as happens where the crust is squeezed. The Chelungpu fault, which ruptured in the 1999 Chi-Chi earthquake, is a thrust fault dipping at about 30°. Read more →

Tsunami

A sequence of very long sea waves set off by a large disturbance, most often a sudden movement of the sea floor during an earthquake, but also by volcanic eruptions or landslides. In Taiwan the CWA issues tsunami information, about 20 minutes after an earthquake that could cause one, for coasts where the estimated wave height reaches its threshold. Read more →

Tuned mass damper TMD

A large mass mounted high in a building, tuned to the building’s natural rhythm of sway and connected to it through shock absorbers; it moves out of step with the tower and turns the energy of the motion into heat. Taipei 101’s damper is a steel sphere 5.5 metres across, built from 41 plates, hanging between the 87th and 92nd floors; sources give its mass as 600 tonnes, 660 tonnes or 730 US tons. Read more →

Typhoon

A strong tropical cyclone in the western North Pacific; the same kind of storm is called a hurricane in the North Atlantic. Under the WMO classification a tropical depression becomes a named tropical storm above 63 km/h and a typhoon when its maximum sustained wind exceeds 116 km/h (63 knots). Around 3 to 5 typhoons a year affect the vicinity of Taiwan. Read more →

Typhoon Committee ESCAP/WMO

An intergovernmental body of 14 members in the western North Pacific region that, among other things, maintains the common list of 140 typhoon names in use since 2000; each member contributed 10. It can retire names and approve replacements, as it did at its 58th session in March 2026. Read more →

Typhoon warning sea and land

The CWA’s official alerts for an approaching typhoon, issued separately for the sea and for land. The warning is tied to the time when the typhoon’s radius of 30-knot winds (about 56 km/h, force 7 on the Beaufort scale) is expected to reach land, with 18 hours as the threshold; bulletins then follow every hour. Read more →

Wind speed probability

A CWA forecast product showing how likely a place is to be reached by a typhoon’s radius of 30-knot winds: 80% means that in 80 of 100 similar forecasts it was. It covers up to 120 hours ahead and is updated every 6 hours, but it does not say how strong the wind and rain will be. Read more →

Sources checked on: 3 November 2026