An earthquake – also called a quake, tremor, or temblor – is the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they cannot be felt, to those violent enough to propel objects and people into the air, damage critical infrastructure, and wreak destruction across entire cities. The seismic activity of an area is the frequency, type, and size of earthquakes experienced over a particular time. The seismicity at a particular location in the Earth is the average rate of seismic energy release per unit volume.
In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic forces, with the largest forming the boundaries between the plates, such as the megathrust faults of subduction zones or transform faults. Energy release associated with rapid movement on active faults is the cause of most earthquakes. Faults may also displace slowly, by aseismic creep.
A fault scarp is a small step-like offset of the ground surface in which one side of a fault has shifted vertically in relation to the other. The topographic expression of fault scarps results from the differential erosion of rocks of contrasting resistance and the displacement of land surface by movement along the fault. Differential movement and erosion may occur either along older inactive geologic faults, or recent active faults.
In geology, aseismic creep or fault creep is measurable surface displacement along a fault in the absence of notable earthquakes. Aseismic creep may also occur as "after-slip" days to years after an earthquake. Notable examples of aseismic slip include faults in California.
Paleoseismology looks at geologic sediments and rocks, for signs of ancient earthquakes. It is used to supplement seismic monitoring, for the calculation of seismic hazard. Paleoseismology is usually restricted to geologic regimes that have undergone continuous sediment creation for the last few thousand years, such as swamps, lakes, river beds and shorelines.
In geology, shear is the response of a rock to deformation usually by compressive stress and forms particular textures. Shear can be homogeneous or non-homogeneous, and may be pure shear or simple shear. Study of geological shear is related to the study of structural geology, rock microstructure or rock texture and fault mechanics.
A fracture is any separation in a geologic formation, such as a joint or a fault that divides the rock into two or more pieces. A fracture will sometimes form a deep fissure or crevice in the rock. Fractures are commonly caused by stress exceeding the rock strength, causing the rock to lose cohesion along its weakest plane. Fractures can provide permeability for fluid movement, such as water or hydrocarbons. Highly fractured rocks can make good aquifers or hydrocarbon reservoirs, since they may possess both significant permeability and fracture porosity.
Geodynamics is a subfield of geophysics dealing with dynamics of the Earth. It applies physics, chemistry and mathematics to the understanding of how mantle convection leads to plate tectonics and geologic phenomena such as seafloor spreading, mountain building, volcanoes, earthquakes, faulting. It also attempts to probe the internal activity by measuring magnetic fields, gravity, and seismic waves, as well as the mineralogy of rocks and their isotopic composition. Methods of geodynamics are also applied to exploration of other planets.
The 1663 Charlevoix earthquake occurred on February 5 in New France, and was assessed to have a moment magnitude of between 7.3 and 7.9. The earthquake occurred at 5:30 p.m. local time and was estimated to have a maximum perceived intensity of X (Extreme) on the Mercalli intensity scale. The main shock epicentre is suggested to have occurred along the Saint Lawrence River, between the mouth of the Malbaie River on the north and the mouth of the Ouelle River on the south. A large portion of eastern North America felt the effects. Landslides and underwater sediment slumps were a primary characteristic of the event with much of the destruction occurring near the epicentral region of the St. Lawrence estuary and also in the area of the Saguenay Graben.
This is a list of articles related to plate tectonics and tectonic plates.
The 1986 Chalfant Valley earthquake struck southern Mono County near Bishop and Chalfant, California at Pacific Daylight Time on July 21. With a moment magnitude of 6.2 and a maximum Mercalli intensity of VI (Strong), the shock injured two people and caused property damage estimated at $2.7 million in the affected areas. There was a significant foreshock and aftershock sequence that included a few moderate events, and was the last in a series of three earthquakes that affected southern California and the northern Owens Valley in July 1986.
The Japan Trench Fast Drilling Project (JFAST) was a rapid-response scientific expedition that drilled oceanfloor boreholes through the fault-zone of the 2011 Tohoku earthquake. JFAST gathered important data about the rupture mechanism and physical properties of the fault that caused the huge earthquake and tsunami which devastated much of northeast Japan.
With the development of both conventional and unconventional resources in Canada, induced seismicity caused by anthropological activities has been observed, documented, and studied.
The Chihshang fault is an active reverse fault system located in the center of the Longitudinal Valley, and is a segment of the Longitudinal Valley Fault. The fault strikes north-northeast–south-southwest, situated between the Central Mountain Range and the Hai'an Range. It lies within the active major collision zone between the Philippine Sea and Eurasian plates. The Chihshang fault extends for about 35 km, from Yuli in the north to Kuanshan in the south. The Chihshang fault remains active. It is thought to be actively creeping as has continuously created cracks and fractures in walls and buildings. The Chihshang fault has a high slip rate of about 2–3 cm/year, and a 4 cm/year creep rate at the dip-slip direction approximately.
Microcracks in rock, also known as microfractures and cracks, are spaces in rock with the longest length of 1000 μm and the other two dimensions of 10 μm. In general, the ratio of width to length of microcracks is between 10−3 to 10−5.
Fault zone hydrogeology is the study of how brittlely deformed rocks alter fluid flows in different lithological settings, such as clastic, igneous and carbonate rocks. Fluid movements, that can be quantified as permeability, can be facilitated or impeded due to the existence of a fault zone. This is because different mechanisms that deform rocks can alter porosity and permeability within a fault zone. Fluids involved in a fault system generally are groundwater and hydrocarbons.
The Cedar Mountain earthquake of 1932 was one of the largest seismic events in the US state of Nevada. The 7.3 earthquake struck at Cedar Mountain in Western Nevada. Shaking was felt as far as Oregon, Southern California, and the Rocky Mountains area. Nevada is the third most seismically active state in the United States due to ongoing rifting occurring within the North American Plate. Extension or thinning of the crust has resulted in numerous faults accommodating strain, at the same time, producing earthquakes. Since the earthquake occurred in a remote part of the state, damage was limited and no deaths were reported.
The 1968 Borrego Mountain earthquake occurred on April 8, at 18:28 PST in the geologically active Salton Trough of Southern California. The Salton Trough represents a pull-apart basin formed by movements along major faults. This region is dominated by major strike-slip faults one of them being the San Jacinto Fault which produced the 1968 earthquake. The mainshock's epicenter was near the unincorporated community of Ocotillo Wells in San Diego County. The moment magnitude (Mw ) 6.6 strike-slip earthquake struck with a focal depth of 11.1 km (6.9 mi). The zone of surface rupture was assigned a maximum Modified Mercalli intensity (MMI) of VII.
This article is intended to provide an overview of various aspects of the tectonics on icy moons.
The 1870 Charlevoix earthquake occurred on 20 October in the Canadian province of Quebec. It had a moment magnitude of 6.6 Mw and a Modified Mercalli intensity rating of X (Extreme). The town of Baie-Saint-Paul was seriously damaged by the event, with the loss of six lives. Effects from the earthquake were felt as far as Virginia and along the New England coast of the United States.
