Earthquake

Earthquake epicenters occur mostly along tectonic plate boundaries, and especially on the Pacific Ring of Fire.
Global plate tectonic movement
Aerial photo of the San Andreas Fault in the Carrizo Plain, northwest of Los Angeles
Comparison of the 1985 and 2017 earthquakes on Mexico City, Puebla and Michoacán/Guerrero
Collapsed Gran Hotel building in the San Salvador metropolis, after the shallow 1986 San Salvador earthquake
Magnitude of the Central Italy earthquakes of August and October 2016 and January 2017 and the aftershocks (which continued to occur after the period shown here)
The Messina earthquake and tsunami took as many as 200,000 lives on December 28, 1908, in Sicily and Calabria.
1755 copper engraving depicting Lisbon in ruins and in flames after the 1755 Lisbon earthquake, which killed an estimated 60,000 people. A tsunami overwhelms the ships in the harbor.
Damaged buildings in Port-au-Prince, Haiti, January 2010.
Ruins of the Għajn Ħadid Tower, which collapsed in an earthquake in 1856
Fires of the 1906 San Francisco earthquake
The tsunami of the 2004 Indian Ocean earthquake
Earthquakes (M6.0+) since 1900 through 2017
Earthquakes of magnitude 8.0 and greater from 1900 to 2018. The apparent 3D volumes of the bubbles are linearly proportional to their respective fatalities.
An image from a 1557 book depicting an earthquake in Italy in the 4th century BCE

Shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves.

- Earthquake

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Lithosphere

Rigid, outermost shell of a terrestrial-type planet or natural satellite.

The tectonic plates of the lithosphere on Earth
Earth cutaway from center to surface, the lithosphere comprising the crust and lithospheric mantle (detail not to scale)
Different types of lithosphere

Subducting lithosphere remains rigid (as demonstrated by deep earthquakes along Wadati–Benioff zone) to a depth of about 600 km.

Seismic wave

Body waves and surface waves
p-wave and s-wave from seismograph
Velocity of seismic waves in Earth versus depth. The negligible S-wave velocity in the outer core occurs because it is liquid, while in the solid inner core the S-wave velocity is non-zero
The sense of motion for toroidal 0T1 oscillation for two moments of time.
The scheme of motion for spheroidal 0S2 oscillation.Dashed lines give nodal (zero) lines. Arrows give the sense of motion.
Earthquake wave paths
The hypocenter/epicenter of an earthquake is calculated by using the seismic data of that earthquake from at least three different locations. The hypocenter/epicenter is found at the intersection of three circles centered on three observation stations, here shown in Japan, Australia and the United States. The radius of each circle is calculated from the difference in the arrival times of P- and S-waves at the corresponding station.
P- and S-waves sharing with the propagation

Seismic waves are waves of energy that travel through Earth's layers, and are a result of earthquakes, volcanic eruptions, magma movement, large landslides and large man-made explosions that give out low-frequency acoustic energy.

Transform fault

Fault along a plate boundary where the motion is predominantly horizontal.

Diagram showing a transform fault with two plates moving in opposite directions
Transform fault (the red lines)
Spreading center and strips
Spreading to upper NEW
Upper to upper
Spreading centers constant
Upper to down NEW
Down to down NEW
Spreading to Down NEW
The Southern Alps / Kā Tiritiri o te Moana rise dramatically beside the Alpine Fault on New Zealand's West Coast. About 500 kilometres (300 mi) long; northwest at top.

Slip along transform faults does not increase the distance between the ridges it separates; the distance remains constant in earthquakes because the ridges are spreading centers.

Megathrust earthquake

Forced underneath another.

Diagram of a subduction zone. The megathrust fault lies on the top of the subducting slab where it is in contact with the overriding plate.
Cross-sectional illustration of normal and reverse faults

Since 1900, all earthquakes of magnitude 9.0 or greater have been megathrust earthquakes.

Focal mechanism

USGS focal mechanism for the 2004 Indian Ocean earthquake

The focal mechanism of an earthquake describes the deformation in the source region that generates the seismic waves.

Subduction

Geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries.

Diagram of the geological process of subduction
The Juan de Fuca plate sinks below the North America plate at the Cascadia subduction zone
Oceanic plates are subducted creating oceanic trenches.
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Earthquakes are common along the subduction zone, and fluids released by the subducting plate trigger volcanism in the overriding plate.

Tsunami

Series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake.

The 2004 Indian Ocean tsunami at Ao Nang, Krabi Province, Thailand
Tsunami aftermath in Aceh, Indonesia, December 2004.
Lisbon earthquake and tsunami in November 1755.
When the wave enters shallow water, it slows down and its amplitude (height) increases.
The wave further slows and amplifies as it hits land. Only the largest waves crest.
An illustration of the rhythmic "drawback" of surface water associated with a wave. It follows that a very large drawback may herald the arrival of a very large wave.
Diagram showing several measures to describe a tsunami size, including height, inundation and run-up.
Calculated travel time map for the 1964 Alaska tsunami (in hours)
One of the deep water buoys used in the DART tsunami warning system
A seawall at Tsu, Mie Prefecture in Japan
Drawing of tectonic plate boundary before earthquake
Over-riding plate bulges under strain, causing tectonic uplift.
Plate slips, causing subsidence and releasing energy into water.
The energy released produces tsunami waves.
Tsunami hazard sign at Bamfield, British Columbia
A tsunami warning sign in Kamakura, Japan
A Tsunami hazard sign (Spanish - English) in Iquique, Chile.
alt=Photo of evacuation sign|Tsunami Evacuation Route signage along U.S. Route 101, in Washington

Earthquakes, volcanic eruptions and other underwater explosions (including detonations, landslides, glacier calvings, meteorite impacts and other disturbances) above or below water all have the potential to generate a tsunami.

Epicenter

The epicenter is directly above the earthquake's hypocenter (also called the focus).

The epicenter, epicentre or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates.

Seismometer

A Kinemetrics seismograph, formerly used by the United States Department of the Interior.
Basic horizontal-motion seismograph. The inertia of the round weight tends to hold the pen still while the base moves back and forth.
Replica of Zhang Heng's seismoscope Houfeng Didong Yi
Milne horizontal pendulum seismometer. One of the Important Cultural Properties of Japan. Exhibit in the National Museum of Nature and Science, Tokyo, Japan.
Simplified LaCoste suspension using a zero-length spring
CMG-40T triaxial broadband seismometer
Seismometer without housing; presented during a demonstration for children about earthquakes at Alfred Wegener Institute.
A low-frequency 3-direction ocean-bottom seismometer (cover removed). Two masses for x- and y-direction can be seen, the third one for z-direction is below. This model is a CMG-40TOBS, manufactured by Güralp Systems Ltd and is part of the Monterey Accelerated Research System.
Viewing of a Develocorder film
Matsushiro Seismological Observatory

A seismometer is an instrument that responds to ground noises and shaking such as caused by earthquakes, volcanic eruptions, and explosions.

Aseismic creep

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In geology, aseismic creep or fault creep is measurable surface displacement along a fault in the absence of notable earthquakes.