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What damage can earthquakes do? Earthquakes can cause damage in the following ways Ground shaking Fault rupture Fault rupture is a relatively rare cause of damage and injury. Landslides Strong ground shaking is a major cause of landslides in New Zealand. Such ice cracks can sometimes be detected by a seismograph if it is located close to the body of water.
Seismic trace of a typical frost quake recorded on the vertical component of the seismic station in Sadowa, Ontario, near Georgian Bay SADO , January 18, at pm, a very cold night 12 frost quakes were recorded within 2 hours that night. A seismologist immediately recognizes the nature of such an event by the single frequency contained in the record. No, there are no months that have more earthquakes than others. Examining the list of Canadian or global earthquakes, there isn't a season that stands out as having an increased number of earthquakes.
The explanation for this can be found by considering that the mechanisms that cause earthquakes are independent of seasonal temperature changes see effects of cold temperatures on earthquakes , and independent of the changes in position of the Earth in the solar system at different times of the year. It is internal geological forces that play the most important role in generating earthquakes. Most large earthquakes are as a result of immense continental plates, called tectonic plates, that move, one with respect to another.
The driving force for this movement is found in the Earth's mantle in the form of convective currents. These currents carry the tectonic plates around the Earth generating earthquakes and volcanic eruptions. The movement of the plates creates strain which is then accumulated in faulted areas causing earthquakes.
Both the movement of the plates and the accumulation of strain along faults are continual processes independent of the time of year. Since the distance between the Earth and Sun changes throughout the year due to the elliptical trajectory of the Earth around the Sun, it seems possible that the attractive gravitational forces between the two bodies might cause extra strain in the Earth's crust.
However, strain models have shown that this extra force is insignificant compared to the tectonic force present. Since the temperature and gravitational forces are the only forces changing with the seasons, seasonal effects can be eliminated as a factor in influencing the frequency of earthquakes. See the Modified Mercalli Intensity Scale.
Minor earthquakes have been triggered by human activities such as mining rockbursts and cavity collapse , the filling of reservoirs behind large dams, and the injection of fluids into wells for oil recovery or waste disposal. Large dams hold back enormous quantities of water. Some of this water may penetrate into cracks in the underlying rock, and sometimes this may trigger small earthquakes under or very near the reservoir.
Following an underground nuclear explosion, small earthquakes have often been recorded near the test site. These are due to the collapse of the cavity created by the explosion.
Man-made earthquakes always occur close to the site of the activity. There is no link between human activities like these and earthquakes occurring hundreds or thousands of kilometres away.
No, except for very rare exceptions. Every year, hundreds of earthquakes occur in Canada. Only a very tiny minority of these precede a larger earthquake. Although a large earthquake may be preceded by a foreshock the Saguenay earthquake of November is an example , the occurrence of a small earthquake is not in itself a typical sign. Hundreds of small earthquakes occur every year in Canada, whereas major earthquakes have occurred only a few times in this century. A small earthquake, however, provides an ideal opportunity to offer reminders about safety measures to take before, during and after an earthquake.
Magnitude is a measure of the amount of energy released during an earthquake. It is frequently described using the Richter scale. To calculate magnitude, the amplitude of waves on a seismogram is measured, correcting for the distance between the recording instrument and the earthquake epicentre. Since magnitude is representative of the earthquake itself, there is only one magnitude per earthquake.
Taking the Saguenay QU earthquake of November 25, as an example, one could not therefore speak of magnitude 6 at Quebec City and magnitude 4 to 5 at Montreal. The effects or intensities experienced at different places were different, but the magnitude of the earthquake is unique; in this example, it was 6 on the Richter scale.
Magnitude thus has more to do with the effects of the earthquake overall. The magnitude scale is logarithmic. This means that, at the same distance, an earthquake of magnitude 6 produces vibrations with amplitudes 10 times greater than those from a magnitude 5 earthquake and times greater than those from a magnitude 4 earthquake. In terms of energy, an earthquake of magnitude 6 releases about 30 times more energy than an earthquake of magnitude 5 and about times more energy than an earthquake of magnitude 4.
The Intensity scale is designed to describe the effects of an earthquake, at a given place, on natural features, on industrial installations and on human beings. The intensity differs from the magnitude which is related to the energy released by an earthquake. Without going into the seismological details, the magnitude defined by Charles Richter is the source of all magnitude scales.
Over the years however, it was realized that the magnitude that Richter had defined for California M L means local magnitude , did not apply to Eastern North America where the seismic waves attenuate differently. Otto Nuttli, a seismologist at the University of Saint-Louis in the United States, developed a magnitude formula which corresponded better to the reality of Eastern America.
One of the formulas which Nuttli derived is used to measure the seisms of Eastern Canada. The formulation used is called Magnitude Nuttli or m N. In order to simplify communication with the public, Canadian seismologists will often refer to the Richter magnitude whereas strictly speaking the seisms that occur in Eastern Canada are measured according to the Nuttli magnitude.
An exception exists for the very small earthquakes of the Charlevoix Region, where the Richter scale is used. Around the world other scales of magnitude exist according to the source conditions of the earthquakes depth , the conditions of attenuation, the type of measured wave, etc. More and more, seismologists describe earthquakes according to the magnitude of the moment scale M W or M. No, it is not an error. As magnitude calculations are based on a logarithmic scale, a ten-fold drop in amplitude decreases the magnitude by 1.
Let us assume that on a seismogram:. Naturally, a negative magnitude is found only for very small events, which are not felt by humans. Though theoretically there is no mathematical limit with the magnitude calculation, physically there is a limit. The magnitude is related to the surface area of the blocks of rock which rub together and in doing so give rise to seismic waves.
Since the tectonic plates have finite dimensions, the magnitude must therefore also reach a maximum. It is believed that the greatest earthquakes can reach magnitude 9. This is difficult to answer absolutely. According to past earthquakes , one can however draw up some general information for Eastern Canada.
Though seismologists generally refer to magnitude on the Richter scale, several magnitude scales do exist. Global Frequency of Earthquakes. In addition to the international networks which can detect earthquakes of magnitude 5. No, earthquakes occur at more or less at the same rate every year. For more info: USGS web site. The greatest earthquake of recent history is the Chilean earthquake of May 22, , which is estimated at magnitude 9.
According to the USGS , this earthquake caused the death of more than people in Chile, in addition to generating a tsunami which propagated around the Pacific, adding several hundreds of victims to the assessment. The greatest world earthquakes since are described on the USGS site. That is about 11 per day! Earthquakes occur across much of Canada. Most earthquakes occur along the active plate boundaries off the British Columbia coast, and along the northern Cordillera southwestern corner of the Yukon Territory and in the Richardson Mountains and Mackenzie Valley and arctic margins including Nunavut and northern Quebec.
Earthquakes also occur frequently in the Ottawa and St. Lawrence Valleys, in New Brunswick, and the offshore region to the south of Newfoundland. Some of the world's largest earthquakes have occurred here see next question. The largest earthquake recorded during historic times in Canada was a magnitude 8.
This earthquake larger than the San Francisco earthquake ruptured a km-long segment of the Queen Charlotte fault and was felt over almost all of British Columbia, and as far north as the Yukon Territory and as far south as Oregon State. Although not recorded by seismographs, the largest earthquake ever to strike Canada was undoubtedly the giant megathrust subduction zone earthquake of off the west Coast of Vancouver Island.
Every day! The resulting cone-shaped mounds are variously known as sand volcanoes, sand boils, or sand blows. For three days, the blaze spread through the city until fire fighters contained it by blasting a fire break. As hot air rose, cool air rushed in, creating wind gusts of over mph, which stoked the blaze and incinerated , people.
Just before a. The break started at the hypocentre and then propagated north at 2. This slip triggered a great earthquake MW 9. Because the area that rose was so broad, the volume of displaced water was immense. As a consequence, a tragedy of an unimaginable extent was about to unfold. The displacement can be due to an earthquake, submarine landslide, or volcanic explosion.
Tsunami is a Japanese word that translates literally as harbour wave, an apt name because tsunamis can be particularly damaging to harbour towns. Regardless of cause, tsunamis are very different from familiar, wind-driven storm waves. Large wind-driven waves can reach heights of 10 to 30 meters in the open ocean. But even such monsters have wavelengths of only tens of meters, and thus contain a relatively small volume of water. In contrast, although a tsunami in deep water may cause a rise in sea level of at most only a few tens of centimetres a ship crossing one wouldn't even notice tsunamis have wavelengths of tens to hundreds of kilometres and an individual wave can be several kilometres wide, as measured perpendicular to the wave front.
Thus, the wave involves a huge volume of water. In simpler terms, we can think of the width of a tsunami, in map view, as being more than times the width of a wind-driven wave.
Because of this difference, a storm wave and a tsunami have very different effects when they strike the shore. The top of the wave may fall over the front of the wave and cause a breaker. In , a number of major pipeline breaks occurred in the city of San Francisco during the earthquake because of lateral spreading. Breaks of water mains hampered efforts to fight the fire that ignited during the earthquake.
Thus, rather inconspicuous ground-failure displacements of less than 7 feet were largely responsible for the devastation to San Francisco in Flow failures, consisting of liquefied soil or blocks of intact material riding on a layer of liquefied soil, are the most catastrophic type of ground failure caused by liquefaction.
These failures commonly move several tens of feet and, if geometric conditions permit, several tens of miles. Flows travel at velocities as great as many tens of miles per hour. Flow failures usually form in loose saturated sands or silts on slopes greater than 3 degrees. Flow failures can originate either underwater or on land. Many of the largest and most damaging flow failures have taken place underwater in coastal areas. For example, submarine flow failures carried away large sections of port facilities at Seward, Whittier, and Valdez, Alaska, during the Prince William Sound earthquake.
These flow failures, in turn, generated large sea waves that overran parts of the coastal area, causing additional damage and casualties. Flow failures on land have been catastrophic, especially in other countries. For example, the Kansu, China, earthquake induced several flow failures as much as 1 mile in length and breadth, killing an estimated , people.
Loss of Bearing Strength - When the soil supporting a building or some other structure liquefies and loses strength, large deformations can occur within the soil, allowing the structure to settle and tip. The most spectacular example of bearing-strength failures took place during the Niigata, Japan, earthquake. During that event, several four-story buildings of the Kwangishicho apartment complex tipped as much as 60 degrees.
Most of the buildings were later jacked back into an upright position, underpinned with piles, and reused. Soils that liquefied at Niigata typify the general subsurface geometry required for liquefaction-caused bearing failures: a layer of saturated, cohesionless soil sand or silt extending from near the ground surface to a depth of about the width of the building.
Past experience has shown that several types of landslides take place in conjunction with earthquakes. The most abundant types of earthquake induced landslides are rock falls and slides of rock fragments that form on steep slopes. Shallow debris slides forming on steep slopes and soil and rock slumps and block slides forming on moderate to steep slopes also take place, but they are less abundant.
Reactivation of dormant slumps or block slides by earthquakes is rare. Large earthquake-induced rock avalanches, soil avalanches, and underwater landslides can be very destructive. Rock avalanches originate on over-steepened slopes in weak rocks. One of the most spectacular examples occurred during the Peruvian earthquake when a single rock avalanche killed more than 18, people; a similar, but less spectacular, failure in the Hebgen Lake, Montana, earthquake resulted in 26 deaths.
Soil avalanches occur in some weakly cemented fine-grained materials, such as loess, that form steep stable slopes under non-seismic conditions. Many loess slopes failed during the New Madrid, Missouri, earthquakes of Underwater landslides commonly involve the margins of deltas where many port facilities are located. The failures at Seward, Alaska, during the earthquake are an example.
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