251 Fun Facts About Earthquakes

Which scale replaced the Richter scale as the standard for measuring big earthquakes?

Moment magnitude is based on how far a fault slips and over what area, so unlike older scales it doesn't saturate for great quakes.

What is the geological term for the point within the Earth where an earthquake rupture first occurs?

The hypocenter, also called the focus, is the point where the rupture starts; plotting many hypocentres maps a fault plane underground.

Which type of plate boundary is most commonly associated with the deepest and most powerful earthquakes?

Convergent boundaries, where one plate subducts beneath another, host the deepest and largest earthquakes.

Which seismic wave travels fastest and reaches a recording station first?

P-waves, or primary waves, arrive first, so early-warning systems detect them to send alerts seconds before the slower, destructive waves hit.

Which famous tower's soft soil has helped it survive at least four strong earthquakes?

Pisa's Leaning Tower sits on soil so soft that the tower doesn't sway in step with quake shaking, so the ground that tilted it has also saved it.

Which island lies on the Ring of Fire, the belt where about 90% of the world's earthquakes strike?

Taiwan sits on the Ring of Fire, while Iceland shakes because it straddles the Mid-Atlantic Ridge, where two plates pull apart.

Which famous high-speed trains brake automatically when seismic sensors detect an earthquake?

Shinkansen lines brake automatically on quake alerts, and when one derailed in the 2004 Chūetsu earthquake, none of its 155 passengers was hurt.

Which famous naturalist was ashore at Valdivia when a severe earthquake struck in February 1835?

Charles Darwin felt it on the Beagle voyage, and captain FitzRoy later found mussel beds stranded above high tide: the land had risen by metres.

Which country was devastated by the largest earthquake ever recorded, on 22 May 1960?

Chile's 1960 Valdivia earthquake, magnitude 9.5, is the largest ever instrumentally recorded, and within two days the Cordón Caulle volcano erupted.

What property of secondary seismic waves stops them passing through liquid?

They are transverse, restored by shear stress: particles move at right angles to the wave's travel, and liquids and gases can't resist shear.

The San Andreas Fault runs along the boundary between the North American plate and which other?

The San Andreas separates the Pacific plate from the North American plate; it is a right-lateral strike-slip transform fault whose two sides grind past each other horizontally rather than one diving beneath the other.

What does the Japanese word tsunami literally mean?

Tsunami means 'harbour wave', from tsu (harbour) and nami (wave): fishermen at sea felt nothing pass beneath them and came home to find their harbours wrecked.

Instead of standing in a doorway, what do safety officials tell people indoors to do in an earthquake?

Drop, cover and hold on, ideally under a sturdy table: doorways in modern houses are no stronger than anywhere else and don't shield you from falling objects.

If an aftershock is larger than the main shock, what is the original quake redesignated as?

The earlier quake becomes a foreshock, since labels are fixed only once the whole sequence is known, as with a big shock two days before Japan's 2011 Tōhoku earthquake.

In Japanese mythology, earthquakes are caused by Namazu, a giant example of which animal?

Namazu is a giant catfish said to lie beneath Japan, pinned down by the god Kashima with a stone; when Kashima's guard slips, the catfish thrashes and the earth shakes.

In Greek mythology, which god was held responsible for causing earthquakes?

Poseidon, god of the sea, was also the earth-shaker; Homer calls him Ennosigaios, and Greeks pictured his trident striking the ground to cause earthquakes.

An earthquake one whole magnitude higher releases roughly how much more energy?

About 32 times, so two steps compound to about 1,000: a magnitude 7 quake unleashes roughly the energy of a thousand magnitude 5 quakes.

The AD 132 seismoscope dropped bronze balls from dragons' mouths into the mouths of which creatures?

A ball falling into one of eight bronze toads supposedly showed the direction of a distant quake.

Which Han dynasty scholar is credited with inventing the first seismoscope?

Zhang Heng built his bronze seismoscope in AD 132; he was also an astronomer and mathematician who catalogued around 2,500 stars.

In December 2018, which mission became the first to place a seismometer on the surface of another planet?

InSight set its SEIS seismometer directly on the Martian ground on 19 December 2018, and the mission ended in December 2022 when dust smothered its solar panels.

Intensity scales such as the Modified Mercalli rate an earthquake by what?

Intensity scales like the Modified Mercalli rate observed effects at a given place, from I (not felt) to XII (total destruction), so one quake has many intensities but a single magnitude.

In Norse myth, which bound god causes earthquakes when he writhes as snake venom drips onto his face?

Loki's wife Sigyn catches the venom in a basin, but whenever she leaves to empty it, the drops make him writhe so hard the earth shakes.

Roughly how long is the Ring of Fire tectonic belt?

The Ring of Fire runs about 40,000 km, almost exactly the distance around Earth's Equator.

Which architect's Imperial Hotel in Tokyo was hailed for surviving the 1923 Great Kantō earthquake?

Frank Lloyd Wright spread the legend of an undamaged hotel, but its central section had slumped and several floors bulged.

Which US financial giant's founder moved his cash to San Mateo after the 1906 San Francisco earthquake, so he could keep lending?

Bank of America grew from Giannini's Bank of Italy, whose rivals had to wait weeks to open vaults the fires had overheated.

What caused most of the destruction in San Francisco after the 1906 earthquake, levelling some 25,000 buildings?

Gas-main fires did the damage: more than 30 blazes from ruptured mains burned for days and destroyed about 25,000 buildings on 490 city blocks.

The 2004 Indian Ocean earthquake struck off the west coast of which Indonesian province?

The epicentre lay off the west coast of Aceh, at Sumatra's northern tip; its capital Banda Aceh was the worst-hit city, and the tsunami killed about 228,000 people in 14 countries.

The 2004 Indian Ocean earthquake's rupture ran north from off Sumatra toward which island chain?

It tore toward the Nicobar and Andaman Islands, and scientists call it the Sumatra–Andaman earthquake.

Ten-year-old Tilly Smith recognised the 2004 tsunami's warning signs on a Thai beach thanks to what?

A geography lesson at school two weeks earlier had taught her the signs, and her warning helped clear Mai Khao Beach before the wave hit.

How long did the shaking of the 1960 Valdivia earthquake last?

The Valdivia shaking lasted about 10 minutes as the magnitude 9.5 rupture tore along roughly 800 km of coast.

The 1960 Valdivia earthquake's tsunami devastated which Hawaiian city with 10.7-metre waves?

Hilo, on the Big Island, took waves up to 10.7 metres; 61 people died there, the city's second tsunami catastrophe after the 1946 Aleutian wave.

The 1964 Alaska earthquake, the strongest recorded in North America, is also named for which day?

It struck on Good Friday, 27 March 1964, at 5:36 p.m. local time, and the magnitude 9.2 shaking lasted four minutes and thirty-eight seconds.

The 2011 Tōhoku earthquake moved Japan's main island of Honshu about how far to the east?

GPS showed parts of Honshu moved about 2.4 metres east; the quake also shifted Earth's axis by an estimated 10 to 25 cm and shortened the day by about 1.8 microseconds.

The 2011 Tōhoku earthquake and tsunami, which triggered the Fukushima disaster, is known in Japan by which numerical shorthand for its date?

3.11 is read San ten Ichi-ichi: the quake struck on 11 March, and the tsunami it triggered led to the Fukushima Daiichi nuclear disaster.

The 1755 Lisbon earthquake struck on the morning of 1 November, which is which Christian holy day?

1 November is All Saints' Day; churches were packed with worshippers when the quake struck around 9:40 a.m., and fires and a tsunami together almost destroyed the city.

Which philosopher used the 1755 Lisbon earthquake to attack 'the best of all possible worlds'?

Voltaire mocked Leibnizian optimism through Dr Pangloss in Candide (1759), having already written a 'Poem on the Lisbon Disaster' in 1756; the quake became a landmark in debates about theodicy.

What did the Marquis of Pombal reportedly urge after Lisbon's 1755 earthquake?

'Bury the dead and heal the living' was his reported advice; as looters roamed the ruins, he sent in troops to restore order.

The 1556 Shaanxi earthquake killed so many partly because residents lived in yaodongs, which are what?

Yaodongs are caves dug into loess cliffs, and the quake collapsed many of them and set off landslides that destroyed many more.

The 1556 Shaanxi earthquake, one of the deadliest in history, struck during which Chinese dynasty?

It struck Huaxian on 23 January 1556 in the Jiajing reign of the Ming dynasty; the population loss including migration and famine has been put at 830,000.

The 2010 Haiti earthquake was centred near which town, about 25 km west of Port-au-Prince?

The epicentre lay near Léogâne, about 25 km west of the capital; the magnitude 7.0 quake destroyed landmarks including the Presidential Palace and the National Assembly building.

Which Alaskan city's Turnagain neighbourhood lost dozens of homes to ground failure in the 1964 earthquake?

Anchorage's Turnagain neighbourhood collapsed as the ground beneath it failed, carrying dozens of homes from the bluffs down toward sea level.

What is the branch of seismology that uses geology to study past earthquakes called?

Paleoseismology reads past earthquakes from geology, dating sediment layers that faults have offset; archaeoseismology does the same from damaged ancient buildings.

Which Japanese novelist wrote After the Quake, six stories set in the month after the 1995 Kobe earthquake?

Haruki Murakami grew up in and around Kobe, and in each of the stories the disaster touches the characters only from a distance.

A simple seismometer relies on which property of a suspended mass to measure ground motion?

Inertia keeps the suspended mass nearly still while the frame moves with the ground, so the relative motion between them traces the shaking.

Richter's original 1935 scale was later revised and given what name?

Richter's scale became the local magnitude, ML, because it was calibrated for Southern California quakes recorded within about 600 km.

On the Richter scale, how much larger are seismometer readings for a magnitude 5 than a magnitude 3?

Each whole magnitude step is a tenfold jump in measured wave amplitude, so going from magnitude 3 to 5 makes readings 100-fold larger.

Which geological setting can trap seismic waves and amplify earthquake shaking?

Sedimentary basins trap waves that bounce around in their soft fill, like jelly in a bowl, while bedrock shakes the least.

Roughly how many major tectonic plates is Earth's rigid outer shell broken into?

About 7 is right: the lithosphere is split into seven or eight major plates, depending on how they are defined, plus many minor platelets.

Roughly how far do the fastest-moving tectonic plates travel each year?

The fastest plates move about 10 cm or more a year, while the Mid-Atlantic Ridge spreads only about 2.5 cm a year, about as fast as fingernails grow.

What are the high-friction regions where a fault plane becomes locked called?

Asperities are the rough, locked patches on a fault plane where friction is highest; stress builds there until it exceeds the rock's strength and the patch ruptures.

Which term names the slow, steady fault slip that visibly offsets streets in Hollister, California?

Aseismic creep is fault slip without notable earthquakes, and in Hollister a creeping branch of the San Andreas system has offset streets and bent houses.

Roughly how long is the San Andreas Fault?

The San Andreas runs about 750 miles (1,200 km) through California, a right-lateral transform fault whose two sides slide horizontally past each other.

At which triple junction does the San Andreas Fault terminate in the north?

The Mendocino Triple Junction, off Cape Mendocino, is where three plates meet and the San Andreas gives way to the Cascadia subduction zone.

Which university's football stadium has an active fault running directly beneath its playing field?

UC Berkeley's California Memorial Stadium has a fault running beneath its field, so its 2010–2012 rebuild split it into sections that can move independently.

Which San Francisco ballpark was packed for a World Series game when the 1989 Loma Prieta earthquake struck?

Candlestick Park held some 62,000 fans awaiting Game 3; concrete fell from the upper deck but no one inside was hurt, and play resumed 10 days later.

What is the average annual slip rate along the San Andreas Fault?

The San Andreas slips about 20 to 35 mm a year on average as the plates on either side grind horizontally past each other.

Which famous volcano lies on the Ring of Fire, home to most of the world's active or dormant volcanoes?

Mount St. Helens sits on the Cascade arc of the Ring of Fire, and in 1980 its summit and north face collapsed in a vast landslide.

Which oceanic plate, subducting beneath South America, fuels the Andean stretch of the Ring of Fire?

The Nazca plate dives beneath the South American plate, raising the volcanic Andes and producing the great 1960 Valdivia earthquake.

Up to how wide is the Ring of Fire tectonic belt?

The belt is up to about 500 km wide, yet about 90% of the world's earthquakes, including most of the largest, strike within it.

What do seismologists call two or more main shocks of similar size from the same fault system?

Doublet earthquakes are similar-sized main shocks from one rupture zone, sometimes seconds apart and sometimes years; Turkey's 7.8 and 7.7 quakes in 2023 struck 9 hours apart.

Which famous Istanbul landmark's original dome collapsed after a series of earthquakes in the 550s?

Hagia Sophia's first dome was too flat to carry its load after the quakes, so the rebuilt dome rose about 6 metres higher, the height it keeps today.

Which 2012 film starring Naomi Watts and Ewan McGregor follows a family caught in the 2004 Indian Ocean tsunami?

The Impossible is based on María Belón's family's real ordeal in Thailand, and Naomi Watts earned an Oscar nomination playing the mother.

Which quake is the most widely cited 'success' of earthquake prediction?

Officials evacuated Haicheng, China hours before the February 1975 shock, though later studies doubted that a valid official prediction was ever made.

What stiff vertical panel do engineers build into a structure to resist sideways earthquake loads?

Shear walls are stiff vertical panels of reinforced concrete, masonry or braced timber that resist the sideways forces of wind and earthquakes.

What do base isolators, such as laminated rubber bearings, sit between?

Base isolators of laminated rubber or friction-pendulum bearings sit between a building and its foundation, letting the ground move beneath while the structure sways far less; San Francisco City Hall was retrofitted onto them in the 1990s.

Why do scientists dislike the term 'tidal wave' for a tsunami?

Calling a tsunami a tidal wave misleads because it falsely implies tides cause them, when most tsunamis are set off by undersea earthquakes displacing water.

The term 'liquefied' was first used in soil mechanics after which 1918 event?

Allen Hazen used the term for the 1918 failure of the Calaveras Dam in California, where water pressure in the soil's pores pushed its grains apart.

Seismologists class an earthquake as deep, rather than intermediate, once it starts below what depth?

Deep earthquakes start below 300 km, where hot, high-pressure rock should flow rather than snap, so how they happen is still poorly understood.

Which Japanese seismologist proved in 1928 that earthquakes occur well below the lithosphere?

Kiyoo Wadati's 1928 paper ended the belief that all quakes are shallow, and the sloping band of deep quakes beneath subduction zones now carries his name.

Which California geothermal plant averaged two magnitude-4 quakes a year from 2004 to 2009?

The Geysers is the world's largest geothermal power complex, and the treated wastewater it injects to replenish its steam reservoir triggers small earthquakes.

Which US state's surge of earthquakes since 2009 has been linked to deep injection of oil-industry wastewater?

Oklahoma's induced quakes may go back decades: a 2015 USGS study suggested even the 1952 El Reno earthquake may have been induced by oil-industry activity.

How much bending did Harry Reid find along the San Andreas in the 50 years before 1906?

Comparing old and new surveys, Harry Reid found about 3.2 metres of gradual bending across the San Andreas in the fifty years before 1906, strain released all at once in the quake; this became his elastic-rebound theory.

Harry Fielding Reid, of elastic-rebound fame, was a professor at which university?

Reid spent 35 years teaching and researching at Johns Hopkins in his native Baltimore, and set out elastic-rebound theory in his 1910 report on the 1906 earthquake.

Inge Lehmann is famous for discovering which part of Earth's interior?

Inge Lehmann spotted waves from a 1929 New Zealand earthquake arriving where none were expected, and in 1936 argued they came from a solid inner core; she lived to 104.

The Lehmann discontinuity, about 220 km down, lies in which layer of Earth?

The Lehmann discontinuity sits in the upper mantle, where seismic waves abruptly speed up, and is named for Danish seismologist Inge Lehmann, who found it.

Which film starring Nicolas Cage and Penélope Cruz is set on Cephalonia, the Greek island a 1953 earthquake flattened?

Captain Corelli's Mandolin casts Cage as an Italian officer who falls for a doctor's daughter; the 1953 quake later destroyed almost every house on the island.

In which state was seismologist Charles Richter born?

Charles Richter was born in Ohio in 1900, and his grandfather moved the family to Los Angeles in 1909, which is how he grew up to be a California seismologist.

Andrija Mohorovičić, of Moho fame, was a scientist of which nationality?

Mohorovičić was Croatian, born in 1857 at Volosko near Opatija on the Istrian coast, and led the Zagreb meteorological observatory where he did his seismological work.

Which physicist taught Mohorovičić in Prague?

From 1875 Mohorovičić studied mathematics and physics at Prague, where Ernst Mach, later famous for the Mach number, was among his teachers.

In the 1978 film Superman, which villain aims a missile at the San Andreas Fault?

Lex Luthor, played by Gene Hackman, stole two test missiles for a real estate scheme: sink the western US and turn his desert land into prime coastline.

Luigi Palmieri, who improved the seismograph, took charge of which institution in 1854?

Palmieri directed the Vesuvius Observatory from 1854 and there built the first electromagnetic seismograph, in 1856, to detect and measure ground tremors.

Seismograph pioneer Luigi Palmieri was the first to detect which element on Earth?

Palmieri spotted helium's yellow D3 spectral line in volcanic material in the early 1880s; astronomers had first seen that line in the Sun's spectrum in 1868.

Seismic wave velocity drops sharply at which boundary?

Mantle to outer core is where seismic waves slow sharply and some stop altogether, which is how seismologists know the outer core is liquid.

Which rose-red Nabataean city, carved into the cliffs of southern Jordan, was badly damaged by an earthquake in AD 363?

Petra lost many of its buildings in the AD 363 quake, and the damage hastened the long decline of the old Nabataean trading capital.

In subduction zones, earthquake foci can reach as deep as roughly what?

Earthquakes in subduction zones track the sinking plate down to about 670 km, near the bottom of the mantle transition zone.

Seismologist Hugo Benioff, who mapped sloping bands of deep earthquakes, worked at which institution?

In 1924 Benioff joined the Seismological Laboratory in Pasadena, which Caltech later took over, and designed the Benioff seismograph there, plus a strain instrument that records the stretching of Earth's surface.

What deep seafloor furrow forms where an oceanic plate bends down into a subduction zone?

An oceanic trench forms where the descending plate bends; the Mariana Trench reaches about 11 km below sea level at the Challenger Deep, the deepest point in the oceans.

Roughly how long is the Cascadia subduction zone?

The Cascadia subduction zone runs about 620 miles, from Vancouver Island to Northern California, where the Juan de Fuca plate dives beneath North America.

The Explorer, Juan de Fuca and Gorda plates are remnants of which ancient plate?

They are the northern remnants of the Farallon plate, named for California's Farallon Islands; most of that once-vast plate has already slid beneath North America.

How much did the Juan de Fuca plate slip on average in the 1700 Cascadia earthquake?

The Juan de Fuca plate slipped an average of about 20 metres along a rupture some 1,000 km long, enough to put the 1700 quake's magnitude near 9.

The New Madrid earthquakes reportedly made which river flow backwards?

Witnesses said the Mississippi's current ran backwards as the ground heaved, and uplift across the riverbed briefly created waterfalls.

The New Madrid quakes were the strongest recorded in the contiguous US east of which mountains?

The 1811–12 New Madrid shocks, estimated at magnitude 7 to 8, were the strongest ever recorded in the contiguous US east of the Rockies; the town of New Madrid sits in Missouri's bootheel.

Which Native American leader's alliance took the New Madrid quakes as a sign to support him?

Tecumseh, whose name was translated as 'shooting star', saw the Great Comet of 1811 and the New Madrid quakes read by many Native Americans as omens backing his confederacy.

Reelfoot Lake, formed by the New Madrid earthquakes, lies in which state?

Reelfoot Lake in north-west Tennessee was the Reelfoot River until the quakes turned it into a lake, and its waters now draw wintering bald eagles.

The 1886 Charleston earthquake was felt as far away as which Caribbean island?

The magnitude-7-class Charleston shock of 31 August 1886 was felt as far away as Cuba, Bermuda and Chicago, and killed about 60 people in the city.

The 1933 Long Beach earthquake occurred on which fault?

The magnitude 6.4 shock of 10 March 1933 ruptured the Newport–Inglewood Fault; the collapse of unreinforced school buildings led to California's Field Act on school construction.

Which two medical centers collapsed in the 1971 San Fernando earthquake, causing most deaths?

Olive View and the Veterans Hospital were worst hit, and the ruined veterans' hospital was later demolished and its grounds turned into a park.

The 1989 Loma Prieta earthquake was named after a peak in which mountain range?

Loma Prieta is a peak in the Santa Cruz Mountains south of San Jose; the magnitude 6.9 shock at 5:04 p.m. on 17 October 1989 interrupted the World Series at Candlestick Park.

Which San Francisco neighbourhood suffered heavy liquefaction damage in 1989?

The Marina District, built on 1906 rubble and fill laid for the 1915 exposition, liquefied; buildings collapsed and a fire broke out, and the quake killed 63 people in all.

The 1994 Northridge earthquake's strongest recorded shaking reached roughly what peak ground acceleration?

A station in Tarzana recorded about 1.8 g (1.82 g), shaking nearly twice the pull of gravity and one of the largest ground accelerations observed in a quake at the time.

The 1994 Northridge quake was what type of event?

Northridge was a blind thrust earthquake: the previously unknown thrust fault that slipped never breaks the surface, and its epicentre lay beneath Reseda in the San Fernando Valley.

The 1995 Kobe earthquake's hypocentre lay beneath the northern end of which land mass?

The rupture began beneath the northern tip of Awaji Island, about 20 km from central Kobe, on the Nojima Fault, whose surface break is now preserved in a museum.

The 1923 Great Kantō earthquake's fires were fanned by winds from what?

Winds from a nearby typhoon fanned the flames into firestorms, and a single fire whirl in Tokyo killed tens of thousands of people within minutes.

Which Chinese leader died about six weeks after the 1976 Tangshan earthquake?

Mao Zedong died on 9 September 1976, and many read the disaster through the old belief that great calamities signal a ruler's lost Mandate of Heaven.

The 2008 Sichuan earthquake struck less than three months before which city opened the Summer Olympics?

Beijing opened the Games on 8 August 2008; after the 12 May quake, the Olympic torch relay was suspended during three days of national mourning.

The 2008 Sichuan earthquake's epicentre was about 80 km from which provincial capital?

The epicentre lay in Wenchuan County, about 80 km west-north-west of Chengdu, Sichuan's capital; the magnitude 7.9 quake killed more than 69,000 people.

Mexico City suffered badly in 1985 despite being over 350 km from the epicentre because it sits on what?

Mexico City grew over the soft clay of Lake Texcoco, and that ancient lake bed resonated with the distant quake's waves and amplified the shaking.

Which Mexico City monument's statue crashed down from its tall column in the 1957 earthquake?

The Angel of Independence's Winged Victory statue fell and broke apart on 28 July 1957; it was restored, and the monument reopened in September 1958.

How is the 2010 Chile earthquake commonly known in Chile?

Chileans call it 27F for 27 February 2010, the date the magnitude 8.8 shock struck off central Chile before dawn.

The magnitude 8.8 Chilean earthquake of 2010 is named for which region?

It began off the coast of central Chile's Maule Region, and the shaking and tsunami that followed killed 525 people.

The 2015 Nepal earthquake set off what was then the deadliest disaster on which mountain?

Ice and snow shaken loose from neighbouring Pumori swept Mount Everest's base camp, killing more than 20 people, the worst toll on the mountain on record.

The 2015 Nepal earthquake is also named for which district?

It is also called the Gorkha earthquake, after the district of its epicentre at the village of Barpak, about 80 km north-west of Kathmandu.

The 2005 Kashmir earthquake's epicentre lay closest to which city?

Muzaffarabad, capital of Azad Kashmir, lay near the epicentre and lost about half its buildings; Pakistan's official death toll from the quake was 87,350.

Which building material worsened the death toll of the 2003 Bam earthquake in Iran?

Bam's houses and its ancient citadel, the Arg-e Bam, were largely mud brick, which crumbled in the 26 December 2003 shock; many structures ignored Iran's 1989 seismic code.

The 1999 İzmit earthquake was part of a westward-marching sequence on which structure since 1939?

Since 1939, ruptures on the North Anatolian Fault have stepped westward toward Istanbul, each loading the next segment; İzmit in August 1999 was followed by Düzce that November.

The first of the 2023 Turkey–Syria earthquakes was centred about 35 km west of which city?

The epicentre lay near Pazarcık in Kahramanmaraş province, west of Gaziantep; the magnitude 7.8 shock struck at 4:17 a.m. on 6 February 2023 on the East Anatolian Fault.

Roughly how many aftershocks followed the 2023 Turkey–Syria earthquakes within three months?

About 30,000 aftershocks were recorded within three months, after a second great shock of magnitude 7.5 to 7.7 struck about nine hours after the first.

Which Italian city's 1908 earthquake and tsunami became the deadliest in European history?

About half of Messina's people died on 28 December 1908, and with Reggio Calabria across the strait, the quake and tsunami killed around 120,000.

Which architect's team won the 1965 contest to replan Skopje after its 1963 earthquake?

Kenzo Tange's team won the UN-backed contest, though only parts of the plan were built; the wrecked old railway station now houses the city museum.

The 1977 Vrancea earthquake caused most of its deaths in which capital city?

Of the roughly 1,570 deaths, about 1,400 were in Bucharest, where more than 30 large buildings collapsed.

How much silt did liquefaction produce in Christchurch's eastern suburbs in February 2011?

Liquefaction pushed around 400,000 tonnes of silt up through the eastern suburbs on 22 February 2011; the quake killed 185 people.

The 2010 Canterbury quake in New Zealand is also known by what name?

It is also called the Darfield earthquake, after the town nearest its epicentre about 40 km west of Christchurch; the magnitude 7.1 shock struck at 4:35 a.m.

Which 2016 New Zealand earthquake ruptured more than 20 faults and was called the most complex earthquake ever studied?

The magnitude 7.8 Kaikōura earthquake struck on 14 November 2016 and killed two people, one near the town and one in neighbouring Hurunui District.

New Zealand's deadliest natural disaster, the 1931 quake, is named for which region?

The Hawke's Bay earthquake of 3 February 1931 killed 256 people, flattened Napier and Hastings, and lifted the seabed to turn a lagoon into dry land; it is also called the Napier earthquake.

Which capital city was devastated by an earthquake on 23 December 1972?

Managua, Nicaragua's capital, was wrecked just after midnight on 23 December 1972; between 4,000 and 11,000 people died, and Roberto Clemente was killed flying relief supplies there.

The 1970 Ancash earthquake in Peru triggered the world's deadliest example of what?

The avalanche of ice and rock from Huascarán's north peak buried the town of Yungay, killing at least 20,000 people; the quake killed roughly 70,000 in all.

As of 2025, which 1939 earthquake was tied as the most powerful ever instrumentally recorded in Turkey?

The magnitude 7.8 Erzincan earthquake of December 1939 killed about 33,000 people; only the first great shock of February 2023 has matched its strength in Turkey.

The 1948 Ashgabat earthquake was little reported because of censorship by which government?

The Soviet Union censored news of the quake, which killed somewhere between 10,000 and 110,000 people, among them the mother of future Turkmen leader Saparmurat Niyazov.

The 1988 Armenian earthquake is also named for which town near its source?

It is the Spitak earthquake, after the town nearest the epicentre that was almost wholly destroyed on 7 December 1988; between 25,000 and 50,000 died, and Gyumri, then Leninakan, was badly hit too.

The 1990 Manjil–Rudbar earthquake in Iran struck near which sea?

The 21 June 1990 shock hit Gilan province near the Caspian Sea, killing between 35,000 and 50,000 people and devastating the towns of Manjil and Rudbar.

The 2001 Gujarat earthquake struck on which Indian national holiday?

It struck at 8:46 a.m. on 26 January 2001, Republic Day, while crowds were at parades and school celebrations marking India's 1950 constitution.

Most deaths in the 2001 Gujarat earthquake occurred in which district?

Kutch district, home to the epicentre, accounted for about 18,400 of the roughly 20,000 deaths, and the towns of Bhuj, Anjar and Bhachau were largely flattened.

Which poet publicly rebuked Mahatma Gandhi for calling the 1934 Bihar earthquake divine punishment for untouchability?

Rabindranath Tagore shared Gandhi's fight against untouchability but accused him of superstition for blaming a quake that killed more than 10,000 people.

Which landmark in the US capital stayed closed for nearly three years after cracking in the 2011 Virginia earthquake?

The Washington Monument was left with more than 150 cracks and stayed shut until May 2014.

The 1950 Assam–Tibet earthquake is the largest recorded quake caused by what?

The 15 August 1950 shock, magnitude 8.6 to 8.7, is the largest known earthquake caused by continental collision, where India pushes into Eurasia, rather than by oceanic subduction.

As of 2025, Russia's most powerful recorded earthquake struck off which peninsula in 1952?

The magnitude 8.8–9.0 quake struck off Kamchatka's east coast and its tsunami destroyed Severo-Kurilsk; a magnitude 8.8 shock off Kamchatka in July 2025 did not surpass it.

Which California town's regular magnitude-6 quakes prompted a forecast for one by 1993, though it came in 2004?

Parkfield saw magnitude-6 shocks about every 22 years from 1857 to 1966, so the next was expected by 1993; it finally struck on 28 September 2004.

Roughly how long a stretch of the San Andreas Fault ruptured in the 1857 Fort Tejon earthquake?

About 225 miles (360 km) of the fault tore open, and at magnitude about 7.9 the quake ranks among the greatest ever recorded in the United States.

Until 1906, which earlier California quake was known as the 'Great San Francisco earthquake'?

The 21 October 1868 Hayward Fault earthquake was called the 'Great San Francisco earthquake' until 1906; it destroyed the Alameda County Courthouse in San Leandro and killed about 30 people.

The 1872 Owens Valley earthquake was centred near which town on the east side of the Sierra Nevada?

The 26 March 1872 shock centred near Lone Pine, where 27 people died in collapsed adobe houses; its magnitude, around 7.4 to 7.9, rivalled the 1906 San Francisco quake.

What lake formed in 1959 when a landslide from a Montana shock dammed the Madison River?

Quake Lake, officially Earthquake Lake, rose behind a landslide that buried campers in Madison Canyon; the Army Corps of Engineers then cut a channel through the slide so the lake couldn't burst.

The 2002 Denali earthquake set pools and lakes sloshing as far away as Louisiana and which other state?

Surface waves from the Mw 7.9 Denali quake of 3 November 2002 set water sloshing in lakes and pools as far as Texas and Louisiana, and damaged houseboats on Lake Union in Seattle.

What is Japan's JMA seismic intensity scale known as locally?

Shindo, 'degree of shaking', runs from 0 to 7 with levels 5 and 6 split into lower and upper; values come from ground acceleration and shaking duration, not from the quake's magnitude.

Over what timescale does a slow earthquake release its energy?

A slow earthquake, also called a silent earthquake, releases its energy over hours to months rather than seconds; slow-slip events beneath Cascadia recur roughly every 14 months.

Since 1900, every earthquake of magnitude 9.0 or greater has been what type?

Megathrust quakes strike where one plate dives beneath another; Cascadia's megathrust, for one, is locked at shallow depths until it slips all at once.

An earthquake within a subducting plate is called what?

Intraslab quakes rupture inside the descending slab itself, as in the 2001 Nisqually quake some 50 km beneath Washington, rather than on the interface between plates.

A fault segment that has not slipped for an unusually long time is called a seismic what?

Loma Prieta filled a recognised gap in 1989.

Which Swiss hydrologist promoted the term 'seiche' in 1890 after observing Lake Geneva?

François-Alphonse Forel, the founder of limnology, popularised 'seiche' from 1890 in his studies of Lake Geneva; the word may derive from Latin siccus, 'dry', for the shoreline the oscillation exposes.

What defines an earthquake swarm?

No single quake dominates a swarm, and many swarms are thought to be driven by fluids moving through the Earth's crust.

Which Greek city-state's helots rose in revolt after an earthquake devastated it in 464 BC?

Sparta asked Athens for help against the revolt, then sent the Athenian army home out of distrust, and the rift helped lead to the First Peloponnesian War.

Which mission first detected, but did not confirm, marsquakes in 1976?

Viking 2's seismometer sat on top of the lander and picked up possible marsquakes in 1976, but wind rocking the spacecraft swamped the signal, so none could be confirmed at the time.

The Moho lies at roughly what average depth beneath the continents?

The Moho averages about 35 km beneath the continents but lies only 5 to 10 km below the ocean floor, where the crust is far thinner.

Which Persian king's tomb at Pasargadae is said to be the world's oldest structure isolated against earthquakes?

Cyrus the Great's tomb sits on mortared stone layers designed to shift in a quake, under a polished stone plate that can slide freely.

Photographic examples of 'earthquake lights' came from which 1960s Japanese swarm?

The Matsushiro swarm near Nagano ran from 1965 to 1967 with about a million quakes, and its glowing skies were the first earthquake lights ever captured on film.

Whose 67-yard playoff touchdown run in January 2011 set off a crowd 'quake' that a nearby seismometer recorded?

Marshawn Lynch broke nine tackles for Seattle against New Orleans, and fans' celebrations registered on a nearby seismometer, earning the play its name, the 'Beast Quake'.

The Pacific Tsunami Warning Center is located where in Hawaii?

The PTWC sits on Ford Island in Pearl Harbor, and its partner, the National Tsunami Warning Center, was founded in Palmer, Alaska, after the 1964 Alaska quake.

How often do DART tsunami buoys log data in 'Event Mode'?

Every 15 seconds: in Event Mode a DART station first sends 15-second readings, then 1-minute averages, instead of Standard Mode's 15-minute values.

The 1946 Aleutian tsunami that killed 159 people in Hawaii is known there by which day's name?

It struck on April Fools' Day, 1 April 1946; the waves had already destroyed Alaska's Scotch Cap lighthouse, killing all five keepers, and with no warning system yet, Hawaii got no alert.

What did the order of the 1929 Grand Banks cable breaks reveal?

An undersea landslide: the quake loosed some 200 cubic km of sediment on the continental slope, and it snapped 12 cables one after another as it flowed downhill.

Which emperor took the Byzantine throne the year after the 526 Antioch earthquake?

Justinian I became co-emperor with his uncle Justin I in 527 and poured aid into rebuilding Antioch, where the quake and the fire after it had killed about 250,000.

Which famous city did the 365 Crete earthquake's tsunami strike, leaving great ships on the tops of buildings?

Alexandria, as the Roman historian Ammianus Marcellinus recorded; he also saw a ship driven almost two miles inland in Greece, lying there rotting for years.

Which Syrian city gives its name to the 1138 earthquake long listed among history's deadliest?

Aleppo's quake is often credited with 230,000 deaths, but historians think that figure merges it with other quakes of 1137 and 1139; NOAA's catalogue lists about 600.

The 1693 Sicily earthquake killed almost two-thirds of the population of which city?

Catania lost some two-thirds of its people on 11 January 1693 and was rebuilt as a showpiece of Sicilian Baroque; at an estimated Mw 7.4 the quake is the most powerful in Italy's recorded history.

A 1783 tsunami killed residents sheltering on which Calabrian town's beach?

Scilla, the legendary home of the sea monster Scylla, lost more than 1,500 people when a cliff collapse sent a wave over the beach where they sheltered.

Arica, struck by a great earthquake in 1868, was then part of which country?

Peru held Arica then; the 1868 tsunami there carried the US gunboat Wateree hundreds of yards inland, and the Navy sold the stranded ship.

What is the largest known inland earthquake in the Japanese archipelago?

Mino–Owari, also called the Nōbi earthquake, reached magnitude 8.0 on 28 October 1891 and killed 7,273 people, the largest inland shock known in Japan.

The 1896 Sanriku tsunami struck while villagers celebrated soldiers' return from which war?

Villagers were celebrating troops home from the First Sino-Japanese War, and the weak jolt worried no one; about half an hour later, waves up to 38.2 m killed about 22,000 people.

The 1707 Hōei earthquake was followed 49 days later by the eruption of which volcano?

The Hōei earthquake of 28 October 1707 ruptured the Nankai Trough; 49 days later, on 16 December, Mount Fuji began its Hōei eruption, which showered ash on Edo.

Great earthquakes along the Nankai Trough recur roughly every how many years?

Great Nankai Trough quakes recur roughly every 100 to 200 years and often come in pairs: in 1854 one great shock struck and a second followed the next day.

Japan's 1948 Fukui earthquake devastated a city still recovering from what?

Fukui was still rebuilding from World War II air raids of July 1945 when the 1948 quake flattened it again, killing thousands and destroying more than 36,000 buildings.

The 2016 Kumamoto earthquakes struck which Japanese island?

Kumamoto is on Kyushu, Japan's south-western main island; the April 2016 shaking damaged Kumamoto Castle's roof and walls and brought down the Great Aso Bridge.

On what date did the 2024 Noto earthquake strike Japan's Ishikawa Prefecture?

It struck at 4:10 p.m. on New Year's Day, 1 January 2024, and fires after the shaking burned out the famous morning-market district of Wajima.

Which Ecuadorian city's commercial district, Tarqui, was destroyed in the 2016 earthquake?

Manta, the port city in Manabí province, lost its Tarqui commercial district in the 16 April 2016 magnitude 7.8 quake, which killed at least 676 people across Ecuador.

The 2023 Al Haouz earthquake was Morocco's deadliest since which 1960 disaster?

The Agadir earthquake killed more than 10,000 in 1960; the 8 September 2023 quake, centred near Ighil in the High Atlas, killed nearly 3,000.

The 2021 Haiti earthquake struck which peninsula?

The magnitude 7.2 quake of 14 August 2021 hit Haiti's south-western Tiburon Peninsula around Les Cayes, on the Enriquillo–Plantain Garden fault zone, killing at least 2,248.

A localised tsunami from the 2018 Sulawesi earthquake struck which provincial capital?

Palu, capital of Central Sulawesi, sits at the head of a narrow bay that funnelled the 28 September 2018 tsunami; with liquefaction in Balaroa and Petobo, around 4,340 people died.

Which Italian city's 2009 earthquake led to six scientists being convicted of manslaughter over their reassurances?

L'Aquila's quake killed 308 people; six scientists and a former official were convicted in 2012 for downplaying the risk, but the six scientists were acquitted on appeal in 2014.

Which Italian town, the home of a famous pasta sauce, was left half destroyed by the August 2016 earthquake?

Amatrice, which gave spaghetti all'amatriciana its name, lay near the epicentre; its mayor said half the town was gone, and the quake killed 299 people.

The 1980 Irpinia earthquake, which left 250,000 people homeless, struck which region of southern Italy?

Campania, inland from Naples: three main shocks struck within 80 seconds, each from a different spot, and at least 2,483 people died.

The 1915 Avezzano earthquake, which killed about 30,000, is also named after which basin?

Fucino was once Italy's third-largest lake: the emperor Claudius partly drained it with tunnels, it was fully drained in 1878, and in 1915 Avezzano lost most of its people.

The 1976 Guatemala earthquake ruptured 240 km of which structure?

The 4 February 1976 quake ruptured some 240 km of the Motagua Fault, the boundary between the North American and Caribbean plates, at 3 a.m.; about 23,000 people died.

Which famous bridge lost a 50-foot section of its upper deck in the 1989 Loma Prieta earthquake?

The Bay Bridge's falling section killed one motorist, but the quake's worst toll came nearby in Oakland, where the double-deck Cypress Street Viaduct collapsed.

Homes built of which material may qualify for lower earthquake insurance rates, because they withstand shaking better?

Wood frames are flexible, and well-designed wood buildings have held up well in major earthquakes.

What does a 'shin-taishin' label on a Japanese building tell buyers?

It meets the 1981 quake code: in the 1995 Kobe earthquake, high-rises built to that standard suffered less than older ones, though the rules covered only new buildings.

A tuned mass damper reduces a building's sway by tuning its oscillation to what?

The structure's resonant frequency is the target, so the damper swings out of phase with the building, like the giant pendulum inside Taipei 101.

Where can an earthquake's vertical ground acceleration rival or exceed its horizontal shaking?

Close to large earthquakes the up-and-down jolt can match the sideways shaking; Christchurch's February 2011 quake first logged 2.2 g at a Heathcote Valley school, later revised to 1.37 g.

How do scientists know the great Cascadia earthquake struck on the night of 26 January 1700?

An 'orphan' tsunami recorded in Japan: villages there logged a wave with no quake felt, and working back across the Pacific put the shock at about 9 p.m. on 26 January.

The MSK-64 intensity scale was proposed by scientists from the USSR, East Germany and where?

Medvedev, Sponheuer and Kárník gave it its name; Vít Kárník was a Czech seismologist in Prague, so the 1964 scale came from the USSR, East Germany and Czechoslovakia.

Which famous author was paid 25 cents a word by Collier's to describe San Francisco burning in 1906?

Jack London rode in from his ranch to watch the city burn, and Collier's held its presses as his eyewitness story was telegraphed to New York.

Besides being a volcanologist, Giuseppe Mercalli was what?

Mercalli was ordained a Catholic priest and taught at Milan's seminary; in 1914 he burned to death at home, allegedly after knocking over a paraffin lamp.

Which world-famous opera tenor was woken in his Palace Hotel suite by the 1906 San Francisco earthquake?

Enrico Caruso, in town with the Metropolitan Opera, fled clutching a signed photo of Theodore Roosevelt and vowed never to return.

In 1969 Kiyoo Mogi warned of a possible magnitude-8 quake in which region of Japan?

Mogi pointed to the Tōkai region's regular history of great quakes in 1969, and in 1978 Japan passed a countermeasures act to watch for the expected shock.

Which meteorologist proposed continental drift in 1912?

Alfred Wegener expanded the idea into a 1915 book, then died on the Greenland ice sheet in 1930, long before plate tectonics won geologists over in the 1960s.

Which range, raised as India drove into Asia, lies on the Alpide earthquake belt?

The Himalayas sit on the Alpide belt, which runs from Java and Sumatra through the Mediterranean into the Atlantic and hosts about 17 percent of the largest quakes.

Which Roman town, badly shaken by an earthquake in AD 62, was buried by a volcanic eruption 17 years later?

Pompeii lost temples, houses and parts of its walls in the AD 62 quake, and Seneca recorded that a flock of 600 sheep died in its aftermath.

In 1958, a quake-triggered rockslide sent a megatsunami 524 metres up the slopes of which Alaskan bay?

In Lituya Bay the wave lifted Howard Ulrich's fishing boat, with his seven-year-old son aboard, over the trees, and both survived.

What fixed the time of Jamaica's 1692 Port Royal earthquake at 11:43 a.m.?

A stopped pocket watch from the harbour, recovered by underwater archaeologists, read 11:43; about two-thirds of Port Royal sank into the sea in that quake.

Moonquakes are far weaker than earthquakes, but with little to damp the vibrations, their shaking can last up to how long?

An hour of shaking is possible because the Moon has fewer attenuating factors; Apollo seismometers listened from 1969 until they were switched off in 1977.

In the 2015 disaster film San Andreas, which actor plays a rescue-helicopter pilot trying to save his family?

Dwayne Johnson plays LAFD rescue pilot Ray Gaines, who races from Los Angeles to San Francisco to reach his estranged wife and daughter.

Which ancient thinker's idea of winds trapped in caves gave rise to the 'sultry weather' quake myth?

Aristotle's Meteorologica blamed earthquakes on winds trapped in underground caves, so hot, still 'earthquake weather' was expected beforehand; geologists dismiss any link between weather and quakes.

In the open ocean a tsunami travels at roughly the speed of what?

In deep water a tsunami races along at 700 to 800 km/h, about the speed of a jet airliner, yet stands only tens of centimetres high until it slows and rears up in the shallows.

At about 330 metres per second, earthquake P waves cross air as which familiar kind of wave?

Sound and P waves work the same way, squeezing and stretching whatever they cross, which is why P waves can pass through rock, water and air alike.

Earthquake S waves cannot cross which layer of Earth, leading scientists to conclude it must be liquid?

The outer core stops S waves dead because a liquid cannot be sheared, so stations on the far side of the planet from an earthquake never record them directly.

What does the gap between P-wave and S-wave arrival times tell seismologists about an earthquake?

How far away it was: the gap widens with every kilometre travelled, so for a nearby quake the gap in seconds times eight gives a rough distance in kilometres.

Which toy do teachers stretch out to model both P waves, by pushing it, and S waves, by flicking it sideways?

A Slinky shows both motions: a push sends a squeeze running down the coils like a P wave, while a sideways flick sends a snaking S wave. A rope can only manage the second.

What do seismologists call the region on Earth's far side where no direct S waves from an earthquake arrive?

A shadow zone for direct S waves takes in everything more than about 104 degrees around the globe from an earthquake; P waves leave a narrower empty band of their own.

Which way do rock particles move as a P wave, also called a compressional wave, passes?

Back and forth along it: a P wave squeezes and stretches the rock in the same direction it is travelling, a push-pull motion that even liquids can pass on.

Besides primary, which word do seismologists say the P in an earthquake's P wave can stand for?

Pressure fits because a P wave works by alternately squeezing and stretching the rock in its path; primary and pressure are both accepted readings of the letter.

On which wiggly-line record of ground motion do scientists pick out the separate arrivals of P and S waves?

A seismogram is the record itself, while a seismograph is the instrument that draws it; the earliest ones scratched their lines onto smoked glass or paper.

What is the bending of P waves called when they cross between deep layers of Earth with different densities?

Refraction bends P waves so sharply at one deep boundary that a band of the planet's surface, about 104 to 140 degrees from the quake, receives no direct P waves at all.

P and S waves travel through Earth's interior, not along its surface, making them which class of seismic wave?

Body waves are the two kinds that travel through the planet rather than around it, and they vibrate at higher frequencies than the surface waves that follow them.

S-wave speed depends on a material's density and on which other property, which is zero in every liquid?

Rigidity is a material's resistance to being twisted out of shape, and because liquids have none, an S wave's speed in them falls to zero and the wave dies.

Whether the first P waves push seismographs up or down at stations worldwide reveals what about an earthquake?

The way the fault slipped shows up as a pattern of ups and downs around the globe, which seismologists plot as a two-tone 'beachball' diagram.

A P wave is a chain of squeezed regions, called compressions, alternating with stretched ones known by which name?

Rarefactions, also called dilatations, are where the rock is briefly pulled thinner, and each is followed at once by another squeeze as the wave runs on.

Which British geologist first clearly told P and S wave arrivals apart, in records of the 1897 Assam earthquake?

Richard Oldham found three distinct phases in the records, mostly from stations in Italy, and showed the first two had travelled through the planet rather than around it.

Which French mathematician predicted in 1830 that an earthquake would send out two waves travelling at different speeds?

Siméon Denis Poisson set out the idea in a memoir to the French Academy of Sciences, working purely from mathematics, decades before instruments could test it.

Which German-born seismologist, later Charles Richter's mentor, has the boundary where S waves vanish named after him?

Beno Gutenberg noticed in 1913 that S waves disappear and P waves abruptly change speed at one depth, and he later helped his protégé devise a world-famous scale.

On most earthquake recordings, how do the S waves usually compare in size with the P waves?

Noticeably bigger: S waves shake the ground harder than P waves and do more of the damage, though the surface waves behind them are often larger still.

Building 3D images of Earth's interior from P and S wave travel times is likened to which hospital imaging method?

A CT scan is the closest cousin of seismic tomography: in both, a computer combines readings along many crossing paths into a 3D picture of a hidden interior.

Because P and S waves need rock, water or air to carry them, physicists place them in which family of waves?

Mechanical waves are vibrations of matter itself, so unlike light, P and S waves have nothing to travel through in the vacuum of space.

Emergency planners say an earthquake kit should hold how much water per person for each day?

One gallon, nearly four litres, covers both drinking and sanitation, and the kit should hold enough for several days because the taps may run dry.

If trapped by rubble after an earthquake, people are advised to signal rescuers with which item rather than shouting?

A whistle is the advised signal, along with banging on a pipe or wall, while a shirt held over the mouth keeps the dust out of the lungs.

After an earthquake, officials advise contacting family by which method, as it can be more reliable than phone calls?

A text message may get through when a voice call cannot, and it saves precious battery power while the electricity is out.

What do US officials advise a driver to do, before setting the parking brake, when an earthquake starts?

Pull over and stop, then stay inside the car until the shaking ends, keeping clear of bridges, overpasses, trees and power lines that could come down.

The Red Cross suggests keeping which item in a bag tied to the bed, to prevent a common earthquake injury?

Sturdy shoes guard against cut feet, because a night-time quake leaves bedroom floors strewn with broken glass; a flashlight and spare glasses belong in the bag too.

US emergency planners say a family's earthquake communications plan should include a contact person based where?

In another state: a contact outside the disaster area gives scattered family members one person to check in with, and the plan should also fix a place to meet.

Where do US earthquake guides say heavy and breakable objects should be stored around the home?

On low shelves they have less far to fall, and the same guides say to fasten bookcases, televisions and refrigerators so they cannot topple.

After an earthquake, people are told not to flick light switches or strike matches until the home is checked for what?

A gas leak can be set off by the tiny spark inside an ordinary electrical switch, so the advice is to leave the home and report a suspected leak.

Which room does the US Geological Survey single out as a dangerous place to be during an earthquake?

The kitchen is full of things that can fall on people, so the advice is to get out of it and shelter in a hallway or against an inside wall.

What are wheelchair users advised to do first when an earthquake begins, before covering the head and neck?

Lock the wheels, then bend over and shield the head and neck with the arms or a book, and stay that way until the shaking stops.

Which earthquake surface wave, named after a British mathematician, shakes the ground purely from side to side?

Love waves, worked out on paper by A. E. H. Love in 1911, move the ground entirely horizontally, and their strength fades quickly with depth below the surface.

A long, rhythmic seismic signal called harmonic tremor usually means that what is moving underground?

Magma on the move sets up a drawn-out hum quite unlike an earthquake's sharp jolt, and volcano observatories watch for it as a sign that an eruption may be near.

Monitors can tell an underground nuclear test from an earthquake because the blast's waves do what?

Push out in all directions: an explosion shoves the surrounding rock outward evenly, a signature no natural earthquake produces and one that test-ban treaty monitors rely on.

Oil prospectors make seismic waves with air guns at sea and, on land, with which machines developed in the 1950s?

Vibrating trucks lower a shaker to the ground and send a long, controlled rumble into the earth, rather than the single sharp bang of a dynamite charge.

The faint background hum that seismographs record everywhere on Earth, known as microseisms, is caused mainly by what?

Ocean waves, and to a lesser degree waves on lakes, keep the ground trembling so steadily that the signal can be picked up anywhere on the planet.

Charles Richter based his magnitude scale on which measurement of the seismic waves traced by a standard seismograph?

Their amplitude, the height of the largest wiggle on the trace, is adjusted for the station's distance from the quake so that every observatory arrives at the same figure.

Rock carries seismic waves because it springs back into shape after being deformed, a property known by what name?

Elasticity lets rock hand a vibration on from grain to grain; strain it too far and it breaks instead, which is what starts an earthquake in the first place.

Why do the first earthquake waves at distant stations arrive by a deep path through the mantle?

Speeds are higher at depth, so a longer route through the deep mantle takes less time than a direct one, and the deep-diving wave wins the race.

Which term describes the way seismic waves grow weaker the farther they travel from an earthquake?

Attenuation happens partly because the energy spreads through an ever larger volume of rock and partly because the rock itself soaks some of it up.

Surface waves from the very largest earthquakes can keep doing what before they finally die away?

Circling the globe several times is possible because waves confined to the surface spread in two dimensions, not three, so they weaken far more slowly with distance.

In which type of fault do the two sides slide horizontally past each other, with little or no vertical movement?

Strike-slip faults carry the land sideways, so roads, fences and streams that cross them end up offset; California's San Andreas is the best-known example.

Reverse faults, in which the upper block is pushed up over the lower one, show the crust is being what?

Squeezed and shortened crust has nowhere to go but up, which is why reverse faults turn up where one plate pushes against another, the opposite setting to a normal fault.

A reverse fault whose break slopes at less than about 45 degrees is given which more specific name?

Thrust faults lie at such gentle angles that they push older rocks up and over younger ones, stacking the layers in the wrong order.

On a sloping fault, what do geologists call the block of rock that lies above the fault plane?

The hanging wall is the block above the break: if it has slid down, the fault is normal, and if it has been pushed up, the fault is reverse.

Where the crust is pulled apart, a raised block between faults is a horst; what is the dropped block called?

A graben forms low ground such as a rift valley, and because the faults come in pairs, grabens and horsts are always formed together.

The terms normal fault and reverse fault come from which English industry, where normal faults were the commonest kind?

Coal mining gave geology the terms because miners met so many faults of one kind that they called it normal, and the rarer opposite kind became the reverse.

What name is given to the step in the ground left where a fault's movement has shifted one side vertically?

A scarp marks where one side of a fault has risen or dropped, and repeated earthquakes can build a small step into a steep bluff.

Geologists call a fault dextral when the far side has moved right; which matching term means it has moved left?

Sinistral faults look the same from either bank: whichever side an observer stands on, the ground across the fault has shifted to the left.

Joints and faults are both fractures in rock; what makes a fracture count as a fault?

Its sides have moved: a fault is a fracture with real displacement across it, while a joint is a crack whose two faces have simply stayed put.

Which geophysicist first recognised transform faults, which offset mid-ocean ridges, as a new class of fault?

Tuzo Wilson saw that these faults slip the opposite way to what the offset ridges suggest, because new sea floor is spreading away from each ridge segment.

Which law of optics, named after a Dutch astronomer, also governs how seismic waves bend at boundaries inside Earth?

Snell's law describes how a wave changes direction when its speed changes, so it works for earthquake waves crossing rock layers just as it does for light entering glass.