|
1994 Mascara Earthquake
The 1994 Mascara earthquake occurred on August 18 at 02:13 local time with an epicenter in a rural part of Algeria. The earthquake measured 5.8 on the moment magnitude scale () and had a depth of . It caused the deaths of 171 people, left up to 12,500 homeless, and destroyed thousands of homes in Mascara Province. Many homes were damaged or destroyed due to poor building quality which collapsed on the inhabitants and resulted in a majority of the casualties. The national government launched a rapid response effort in its aftermath. Tectonic setting Northwest Africa, which also includes Algeria, is situated near a complex and poorly defined convergent plate boundary which separates the African Plate from the Eurasian Plate. The converging plates create a zone of compression in northern Algeria, which are accommodated by mainly thrust and strike-slip faults. Thrusting results in the formation of the Atlas Mountains. The tectonic situation of Algeria also makes the country a seis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
West Africa Time
West Africa Time, or WAT, is a time zone used in west-central Africa. West Africa Time is one hour ahead of Coordinated Universal Time ( UTC+01:00), which aligns it with Central European Time (CET) during winter, and Western European Summer Time (WEST) / British Summer Time (BST) during summer. As most of this time zone is in the tropical region, there is little change in day length throughout the year and therefore daylight saving time is not observed. West Africa Time is the time zone for the following countries: * (as Central European Time) * * * * * * (western side only) * * * (as Central European Time) * * * * (as Central European Time) * Countries west of Benin (except Morocco and Western Sahara) are in the UTC±0 time zone. Civil time in most of those countries is defined with reference to Greenwich Mean Time (now an alias for UTC±0, rather than an independent reference). References See also * Central European Time, an equivalent time zone covering most E ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
1980 El Asnam Earthquake
The 1980 El Asnam earthquake occurred on October 10 at with a moment magnitude of 7.1 and a maximum Mercalli intensity of X (''Extreme''). The shock occurred in the Algerian town of El Asnam (now known as Chlef). The shocks were felt over away, with the initial earthquake lasting 35 seconds. It was the largest earthquake in Algeria, and was followed three hours later by a magnitude 6.2 aftershock. The earthquake created about of surface rupture and had a vertical slip of up to . No foreshocks were recorded. The earthquake was found to have occurred very close to the epicenter of the 1954 Chlef earthquake using joint epicenter determination techniques. It occurred at a previously unknown reverse fault. The earthquake was the largest in the Atlas range since 1790. In addition to the earthquake, weak tsunami waves were recorded on tide gauges. The earthquake occurred at a populated region of Algeria, affecting 900,000 people. It destroyed 25,000 houses and made 300,000 inhabit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Seismic Intensity Scales
Seismic intensity scales categorize the intensity or severity of ground shaking (quaking) at a given location, such as resulting from an earthquake. They are distinguished from seismic magnitude scales, which measure the magnitude or overall strength of an earthquake, which may, or perhaps may not, cause perceptible shaking. Intensity scales are based on the observed effects of the shaking, such as the degree to which people or animals were alarmed, and the extent and severity of damage to different kinds of structures or natural features. The maximal intensity observed, and the extent of the area where shaking was felt (see isoseismal map, below), can be used to estimate the location and magnitude of the source earthquake; this is especially useful for historical earthquakes where there is no instrumental record. Ground shaking Ground shaking can be caused in various ways (volcanic tremors, avalanches, large explosions, etc.), but shaking intense enough to cause damage is usuall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unreinforced Masonry Building
An unreinforced masonry building (or UMB, URM building) is a type of building where load bearing walls, non-load bearing walls or other structures, such as chimneys, are made of brick, cinderblock, tiles, adobe or other masonry material that is not braced by reinforcing material, such as rebar in a concrete or cinderblock. The term is used in earthquake engineering as a classification of certain structures for earthquake safety purposes, and is subject to minor variation from place to place. URM structures are vulnerable to collapse in an earthquake. One problem is that most mortar used to hold bricks together is not strong enough. Additionally, masonry elements may "peel" from the building, and fall onto occupants or passersby outside. In California, the 1933 Long Beach earthquake resulted in a near-immediate statewide ban on construction of new unreinforced masonry school buildings. A State law enacted in 1986 required seismic retrofit Seismic retrofitting is the modificat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
El Keurt
El Keurt is a town and commune in Mascara Province, Algeria ) , image_map = Algeria (centered orthographic projection).svg , map_caption = , image_map2 = , capital = Algiers , coordinates = , largest_city = capital , relig .... According to the 1998 census it has a population of 3,536. References Communes of Mascara Province Mascara Province {{MascaraDZ-geo-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Local Magnitude
The Richter scale —also called the Richter magnitude scale, Richter's magnitude scale, and the Gutenberg–Richter scale—is a measure of the strength of earthquakes, developed by Charles Francis Richter and presented in his landmark 1935 paper, where he called it the "magnitude scale". This was later revised and renamed the local magnitude scale, denoted as ML or . Because of various shortcomings of the original scale, most seismological authorities now use other similar scales such as the moment magnitude scale () to report earthquake magnitudes, but much of the news media still erroneously refers to these as "Richter" magnitudes. All magnitude scales retain the logarithmic character of the original and are scaled to have roughly comparable numeric values (typically in the middle of the scale). Due to the variance in earthquakes, it is essential to understand the Richter scale uses logarithms simply to make the measurements manageable (i.e., a magnitude 3 quake factors 1 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Surface Ruptures
A surface, as the term is most generally used, is the outermost or uppermost layer of a physical object or space. It is the portion or region of the object that can first be perceived by an observer using the senses of sight and touch, and is the portion with which other materials first interact. The surface of an object is more than "a mere geometric solid", but is "filled with, spread over by, or suffused with perceivable qualities such as color and warmth". The concept of surface has been abstracted and formalized in mathematics, specifically in geometry. Depending on the properties on which the emphasis is given, there are several non equivalent such formalizations, that are all called ''surface'', sometimes with some qualifier, such as algebraic surface, smooth surface or fractal surface. The concept of surface and its mathematical abstraction are both widely used in physics, engineering, computer graphics, and many other disciplines, primarily in representing the surfaces ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aftershock
In seismology, an aftershock is a smaller earthquake that follows a larger earthquake, in the same area of the main shock, caused as the displaced crust adjusts to the effects of the main shock. Large earthquakes can have hundreds to thousands of instrumentally detectable aftershocks, which steadily decrease in magnitude and frequency according to a consistent pattern. In some earthquakes the main rupture happens in two or more steps, resulting in multiple main shocks. These are known as doublet earthquakes, and in general can be distinguished from aftershocks in having similar magnitudes and nearly identical seismic waveforms. Distribution of aftershocks Most aftershocks are located over the full area of fault rupture and either occur along the fault plane itself or along other faults within the volume affected by the strain associated with the main shock. Typically, aftershocks are found up to a distance equal to the rupture length away from the fault plane. The pattern ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quaternary
The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ago to the present. The Quaternary Period is divided into two epochs: the Pleistocene (2.58 million years ago to 11.7 thousand years ago) and the Holocene (11.7 thousand years ago to today, although a third epoch, the Anthropocene, has been proposed but is not yet officially recognised by the ICS). The Quaternary Period is typically defined by the cyclic growth and decay of continental ice sheets related to the Milankovitch cycles and the associated climate and environmental changes that they caused. Research history In 1759 Giovanni Arduino proposed that the geological strata of northern Italy could be divided into four successive formations or "orders" ( it, quattro ordini). The term "quaternary" was introduced by Jules Desnoye ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Epicenter
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. Surface damage Before the instrumental period of earthquake observation, the epicenter was thought to be the location where the greatest damage occurred, but the subsurface fault rupture may be long and spread surface damage across the entire rupture zone. As an example, in the magnitude 7.9 Denali earthquake of 2002 in Alaska, the epicenter was at the western end of the rupture, but the greatest damage was about away at the eastern end. Focal depths of earthquakes occurring in continental crust mostly range from . Continental earthquakes below are rare whereas in subduction zone earthquakes can originate at depths deeper than . Epicentral distance During an earthquake, seismic waves propagate in all directions from the hypocenter. Seismic shadowing occurs on the opposite s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reverse Fault
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 plane'' is the plane that represents the fracture surface of a fault. A ''fault trace'' or ''fault line'' is a place where the fault can be seen or mapped on the surface. A fault trace is also the line commonly plotted on geologic maps to represent a fault. A ''fault zone'' is a cluster of parallel faults. However, the term is also used for the zone of crushed rock along a single fault. Prolonged motion along closely spaced faults can blur the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Strike And Dip
Strike and dip is a measurement convention used to describe the orientation, or attitude, of a planar geologic feature. A feature's strike is the azimuth of an imagined horizontal line across the plane, and its dip is the angle of inclination measured downward from horizontal. They are used together to measure and document a structure's characteristics for study or for use on a geologic map. A feature's orientation can also be represented by dip and dip direction, using the azimuth of the dip rather than the strike value. Linear features are similarly measured with trend and plunge, where "trend" is analogous to dip direction and "plunge" is the dip angle. Strike and dip are measured using a compass and a clinometer. A compass is used to measure the feature's strike by holding the compass horizontally against the feature. A clinometer measures the features dip by recording the inclination perpendicular to the strike. These can be done separately, or together using a tool such a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
