How does Earthquake happen?

How does Earthquake happen?

A fault slips suddenly, resulting in an earthquake. Although the tectonic plates are constantly moving slowly, the friction causes them to become impermeable at their borders. An earthquake occurs when the stress on the edge exceeds the friction, releasing energy in waves that flow through the earth’s crust and produce the shaking we experience.

The Pacific Plate and the North American Plate are the two plates that makeup California. The majority of the Pacific Ocean’s floor and the California Coastline are both parts of the Pacific Plate. Most of the North American Continent and portions of the Atlantic Ocean’s floor are made up of the North American Plate. The San Andreas Fault serves as the main dividing line between these two plates.

The Science of Earthquakes | U.S. Geological Survey

The San Andreas Fault stretches for more than 650 miles and goes down at least 10 kilometers. The Hayward (Northern California) and San Jacinto (Southern California) faults, for example, branch off of and join the San Andreas Fault Zone.

At a rate of around two inches each year, the Pacific Plate grinds past the North American Plate. There are numerous little shocks and a few moderate earth earthquakes as a result of the San Andreas Fault system’s continual “creep” adaptation to this movement. In other regions where creep is NOT consistent, strain can accumulate over hundreds of years until finally releasing and causing large earthquakes.

The names “foreshock” and “aftershock” are figurative.

Foreshocks are smaller earthquakes that occur in the same place as larger ones. A smaller earthquake in the same region must first occur to classify an earthquake as a foreshock.

Smaller earthquakes known as “aftershocks” are those that happen in the same general location days to years after a bigger event or “mainshock.” They happen between 1-2 fault lengths distant and just before the background seismicity level picks back up. Typically, aftershocks are modest fault readjustments along the part of the fault that shifted during the mainshock. With time, these aftershocks become less frequent. Deep earthquakes (>30 km) historically had a far lower likelihood of being followed by aftershocks than shallow earthquakes.

The crust or upper mantle, which extends from the surface of the planet to a depth of around 800 kilometers, is where earthquakes occur (about 500 miles).

How and why do earthquakes occur? | Newsmobile

The strength of shaking at the surface from an earthquake that happens at 500 km depth is significantly less than if the same earthquake had occurred at 20 km depth because the strength of shaking from an earthquake weakens with increasing distance from the earthquake’s source.

What Causes an Earthquake, and What Happens During a Quake? | Caltech  Science Exchange

Additionally, the depths of earthquakes reveal vital details about the tectonic environment and the structure of the Earth. In subduction zones, where plates are colliding and one plate is being subducted beneath another, this is most obvious.

We may detect characteristics of a subduction zone’s structure, such as how steeply it dips and whether the down-going plate is flat or bent, by carefully mapping the position and depth of earthquakes connected to the zone. We can better understand the mechanics and properties of the deformation in the subduction zone thanks to these specifics, which are crucial.

What Causes an Earthquake, and What Happens During a Quake? | Caltech  Science Exchange

At convergent plate borders, when a thick oceanic plate collides with a less dense continental plate and falls beneath the latter, the deepest earthquakes take place inside the core of subducting slabs, oceanic plates that drop into the Earth’s mantle. The Sumatra 2004 M9.1 event and the Japan 2011 M9.0 earthquake were both produced by the plate boundary contact between two such plates, which is only active to relatively shallow depths of about 60 km. However, in deeper subduction zone situations where oceanic slabs are relatively cold compared to the surrounding mantle, these faults remain brittle and can cause earthquakes to occur as deep as 700 km (e.g., Pacific Plate beneath Japan and Kamchatka, and Tonga).

These earthquakes are produced as a result of rheology changes (variations in viscosity properties) that occur as the slab sinks deeper into the mantle. Cross sections of subduction zones, also referred to as “Wadati-Benioff Zones,” show the trajectory of such events.

Faults are exclusively active within continents and along the continental plate, boundary transform faults like the San Andreas, possibly down to depths of about 20 km.

The Science of Earthquakes | U.S. Geological Survey

Unless there is a seismic station nearby and above the epicenter, accurately identifying the depth of an earthquake is often more difficult than determining its position. Therefore, errors in depth calculations tend to be a little bigger than errors in location calculations. There are numerous places in the United States and many other nations across the world where earthquakes caused by human activity have been reported. A variety of factors, such as the filling of reservoirs, surface and underground mining, the removal of fluids and gas from the subsurface, and the injection of fluids into underground formations, can trigger earthquakes. Larger, possibly dangerous man-made earthquakes have happened in the past, even though the majority of induced earthquakes are tiny and pose minimal risk.

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