Understanding Earthquakes Essay Example

for help with any issues related to water pipes. According to McNally (33), residents of Armenia experienced immense fear and devastation after Colombia was struck by a recent earthquake.

The people were initially shocked by the unexpected earthquake, which had a high magnitude. Authorities reported that Monday's quake, measuring 6.0 on the Richter scale, not only caused destruction to buildings but also triggered landslides (Colombian Earthquake 1).

Therefore, it is clear that sufficient preparation time is necessary for such a significant earthquake.

Regrettably, Colombians had no prior warning about this calamity. The innocent citizens of Armenia mistakenly believed it would be just another ordinary day.

In addition, earthquakes with a magnitude of 5.5 or higher are typically the ones that result in significant damage (Fradin 27).

The earthquake caused extensive devastation, with many individuals becoming trapped under debris. The impact on the affected population was immense, despite the relatively low magnitude of 6.0. The extent of the damage indicates that it was not a minor incident, and numerous lives were deeply affected by this sudden and tragic event.

According to sources, the number of casualties in Armenia is estimated to be over 1,000, possibly even exceeding 2,000 (Whitbeck 2). Numerous individuals experienced the heartbreaking loss of their loved ones and close friends. The sudden transition from happiness to devastation resulted in the death of 2,000 previously joyful individuals. This catastrophe not only claimed lives but also left more than two-thirds of Armenia destroyed, including devastated rural communities. The impact extended beyond human suffering, encompassing injuries and infrastructure damage (Moreno 20).

Practically all of the towns were destroyed by the earthquake, leaving many people without shelter and protection. This catastrophe resulted in loss

of life and homes, leaving numerous individuals with nothing.

Finally, the government's efforts to aid the situation at hand were deemed ineffective. Henry Gomez, the governor, remarked, "We don't have enough coffins to bury the dead" (Whitbeck 3). It is imperative for the government to provide coffins for the deceased as it is a matter of respect. Every individual who has passed away deserves a proper burial to honor their lives. Additionally, there was a lack of coordination between the Red Cross, Civil Defense, and firefighters, with each group being accused of functioning as separate entities (Whitbeck 1). The rescue teams needed to collaborate in order to avoid chaos resulting from disorganization.

During times of genuine need, it is unfair that people choose to be stubborn and unhelpful instead of providing assistance. The government should have fulfilled its obligation by aiding its people. Colombia experienced a devastating earthquake that caused extensive destruction and impacted numerous lives. Since then, the country has been diligently working towards reconstruction and recovery from this tragic event.

Hopefully, the victims of the devastating 1906 San Francisco earthquake can rebuild their shattered lives. The earthquake struck at 5:12 in the morning and claimed the lives of 3000 individuals. It lasted approximately 40 seconds and registered at 8.3 on the Richter Scale, causing panic as people fled their homes or sought refuge within buildings, only to be crushed beneath them. Those who ran into the streets met their demise as towering buildings collapsed upon them. Despite swift action from the fire department, their efforts were hindered by severed water pipes along the San Andreas Fault, leaving them struggling to extinguish flames for several days.

In just

one day, extensive fires erupted throughout the city due to gas mains exploding, resulting in widespread devastation. The city, which was undergoing a major economic expansion, suffered immense destruction. The earthquake caused old buildings to easily collapse and trap people underneath, as they were not constructed to withstand such tremors. Furthermore, sailors attempting to escape the catastrophe were tossed about by powerful waves like mere toys. Buildings made of weak materials like unreinforced brick and wood proved incapable of withstanding the earthquake's magnitude. Consequently, seismic activity caused a 250-mile long portion of the San Andreas Fault to shift, causing significant damage to roads and fences.

The earthquake caused extensive damage to rivers, roads, and power lines. This resulted in the disconnection and misalignment of these infrastructure elements with their surrounding areas. For example, a road that crossed the fault shifted 21 feet northward compared to the road on its eastern side, just like the rivers and creeks did. Los Bonas, located 30km east of the fault, suffered significant destruction. However, towns on the eastern side of San Francisco Bay such as Berkeley (25km east of the fault) experienced minimal damage. Sacramento, California's capital city situated 120km east of the rupture remained unaffected by the seismic event.

Researchers have discovered that the earthquake occurred along a 1170 Km stretch, ranging from north of Oregon to south of Los Angeles. In order to prevent loss of life, future San Francisco structures will be designed to withstand strong earthquakes by allowing them to sway rather than collapse. This earthquake was caused by the movement of the Pacific plate heading north and the North American plate moving south, creating the San

Andreas fault.

The earthquake in San Francisco in 1990 had a magnitude of approximately 8.3 on the Richter scale, but it was not as severe as the earthquake in 1906. An earthquake is characterized by the trembling or shaking movement of the earth's surface. Although most earthquakes are minor tremors, larger ones usually begin with slight tremors and rapidly progress to one or more violent shocks, followed by gradually diminishing vibrations known as aftershocks. The point where an earthquake originates beneath the earth's surface is called its focus, while the epicenter is directly above the focus on the surface. Scales such as the Richter scale and the Mercalli scale determine both the magnitude and intensity of an earthquake.

The primary reason behind earthquakes is the accumulation of stress at the boundaries of the earth's lithospheric plates. When this stress is abruptly discharged along a fault line or fracture in the crust, it leads to movement of rock blocks on both sides of the fault and generates vibrations that propagate as waves through the earth. Additionally, volcanic eruptions, rockfalls, landslides, and explosions can also have an impact on earthquakes; however, their influence is generally confined to specific regions.

There are multiple types of earthquake waves: P (primary) waves, which are compressional and have the highest speed; S (secondary) waves, which are transverse and cause vibrations perpendicular to their direction; and surface waves, including L (long) waves. Variations in density and rigidity affect the speeds of P and S waves, allowing seismologists to differentiate between the Earth's crust, mantle, and core. Seismographs are used to record P, S, and L waves. The absence of S waves at certain depths indicates

that the outer part of the Earth's core is liquid.

Damage caused by earthquakes is most severe in a broad zone surrounding the epicenter. Faults that reach the surface often lead to cracking of the surface ground, resulting in horizontal and vertical displacements of several yards. Such movements can occur during minor earthquakes or even fault creep accompanied by microearthquakes that are too small to be felt. The severity of earthquake vibrations and subsequent damage to an area depends partly on the characteristics of the ground. Unconsolidated surface material, like poorly compacted fill or river deposits, experiences longer-lasting vibrations with greater wave amplitudes, while bedrock areas are less affected. Urban areas with high population density and inadequate structural design to withstand intense shaking suffer the most damage.

Earthquakes have the potential to cause severe damage and loss of life. They can result in destructive vibrations in buildings, breakage of water and gas lines, and uncontrollable fires. The collapse of structures and the propulsion of glass and objects through the air contribute to this damage. Flexibly constructed buildings on bedrock are generally more resistant to earthquake damage than rigid structures on loose soil. Moreover, earthquakes can trigger mudslides in certain areas, which may bury dwellings beneath sliding down mountain slopes.

Coastal cities can be devastated by damaging waves that spread outward from the epicenter of a submarine earthquake. There have been notable earthquakes in Lisbon (1755), Charleston, S.C. (1886), Assam, India (1897 and 1950), California (1906), Messina (1908), Gansu, China (1920), Japan (1923), Chile (1960), Iran (1962), Guatemala (1976), Hebei, China (1976) and Armenia (1988). The earthquakes in Lisbon and Chile were accompanied by tsunami. Alaska experienced one

of the most severe North American earthquakes ever recorded on Good Friday, 1964 with a magnitude of 8.4 to 8.6 on the Richter scale, which not only raised around 70,000 sq mi of land and caused devastation in several cities but also generated tsunami that inflicted damage as far south as California.

In February 1971, an earthquake occurred near Los Angeles on the San Fernando fault, lasting for 10 seconds and resulting in the uplift of mountain parts by 8 feet (2.4 meters). This event caused the death of 64 individuals and $500 million worth of damage.

Another earthquake, called the Loma Prieta earthquake, took place in 1989 above Santa Cruz. It lasted for 15 seconds and had a magnitude of 7.1 on the Richter scale. The quake resulted in the deaths of 67 people and led to the collapse of buildings and bridges.

A severe earthquake struck Managua, Nicaragua's capital, in December 1972, causing almost complete destruction.

In July 1993, a devastating earthquake with a magnitude of 7.8 on the Richter scale occurred in northern Japan.

It is estimated that over the past 4,000 years, earthquakes have caused more than13 million deaths.

Earthquakes occur frequently globally, with many going unnoticed. However, by placing seismograms worldwide, these earthquakes can be identified and recorded. Occasionally, a more powerful earthquake of greater magnitude may happen and cause damage to the affected region. Faults heavily influence the occurrence of earthquakes as they determine their likely location. Hence, faults are the main cause of earthquakes.

The frequency of earthquakes is affected by the type of fault. At a divergent boundary, a mid-ocean ridge forms beneath the ocean surface. This occurs when plates are pulled apart due

to tension. As a result, new oceanic crust is created at the divergent boundary as magma rises and hardens on the sea floor. If the plates on both sides of the divergent boundary continue to move apart, the width of the ocean gradually increases, which is called seafloor spreading. Mid-ocean ridges can be recognized by a valley with crack-like characteristics at the divergent boundary.

The crack-like valley is the result of tension pulling apart the plates, causing multiple instances of normal faulting in the divergent boundary. These normal faults are the source of earthquakes at divergent boundaries. When the tension between the plates reaches a critical point, the oceanic crust will fracture due to the occurrence of many normal faults, as depicted in the diagram. The extension of the crust leads to the formation of these normal faults, which eventually slip vertically when the tension becomes excessive.

The earthquakes at divergent boundaries are caused by the large distance they move in a short time. These boundaries mostly occur on the sea floor, resulting in distributed earthquakes along the boundary. The earthquake distributions at divergent boundaries are shallow because the crust is being pulled apart. This shallow depth is due to normal faulting occurring near the sea floor, caused by tension.

The earthquakes that happen at divergent boundaries are caused by normal faults. The tectonic activity on the seafloor worldwide is especially strong, leading to a large number of earthquakes at mid-ocean ridges. An example illustrating this is the Mid-Atlantic ridge, where the seafloor spreads about 3cm annually. The frequency of earthquakes at a specific mid-ocean ridge depends on the amount of tension present; higher tension results in more

seafloor spreading and a greater occurrence of earthquakes.

The world's water primarily consists of four major oceans: the Atlantic (north and south), the Pacific, the Antarctic, and the Indian Ocean. Earthquakes can happen in these ocean basins at mid-ocean ridges or subduction zones. When there are tensional forces in the Earth's crust, it becomes thinner than normal, leading to a weaker crust if there is no fault present.

In ocean basins, the oceanic crust can experience this phenomenon, but it will only result in an earthquake when there is a hot spot present. A hot spot refers to an anomalous region of the mantle that is experiencing a rise in temperature and provides the lava necessary for volcanic activity. If, simultaneously, a hot spot occurs directly underneath a thinned crust, the magma in the hot spot might experience excessive pressure, which cannot be contained by the thinner and weakened crust. In such scenarios, the magma can penetrate the lithosphere and eventually erupt on the Earth's surface. This upward movement of the magma can trigger earthquakes when it breaks through the crust.

When the crust breaks at the sea bed, it eventually forms a volcanic island in the ocean. Plate movements can create chains of basaltic volcanic islands, like Hawaii. This process has occurred in other parts of the world. The Hawaiian chain does not experience frequent large earthquakes; it is essentially aseismic ridge.

Therefore, the occurrence of earthquakes caused by hot spots in ocean basins is infrequent, and when they do occur, they tend to happen at shallow depths. This can be attributed to the thinning of the crust due to tension, as the origin of the earthquakes is

within the crust.

Subduction zones, on the other hand, occur at convergent boundaries where two plates collide and one is forced beneath the other. These collisions are a result of compression forces that push the plates towards each other.

One plate, such as the Pacific plate, is subducted below another plate, like the Eurasian plate, into the mantle. This subduction allows for the recycling of the plate. Although they desire to move in different directions, the plates are driven to collide with each other. This ongoing force gradually leads to the accumulation of pressure at the plate boundary.

Over time, due to extreme force, one plate will gradually bend downward under the other without slipping. The friction between the plates is sufficient for them to bend without slipping. This movement is slow but steady, possibly only a few millimeters per year. Each movement increases the accumulation of elastic strain energy within the rock.

The rock retains energy for varying periods, ranging from a few decades to several thousand years. An earthquake occurs when the stress on the rocks surpasses their limit. This causes the fault to rupture and undergo rapid movement over a significant distance. Consequently, the plates snap back into a different position, causing the already undercutting plate to further submerge beneath the other. The collision of two plates typically generates substantial forces which, in turn, initiate earthquakes within subduction zones.

The number of earthquakes that occur in Subduction zones is similar to those that occur in the mid-ocean ridges. This is due to the global coverage of tectonic plates. When they separate at one location, one plate sinks beneath another at another location. Consequently, an earthquake triggered at

a divergent boundary also triggers one at a convergent plate. As a result, the frequency of earthquakes in Subduction zones is comparable to that in Mid-ocean ridges, which is significantly high. The earthquakes occurring at convergent boundaries are dispersed across various points.

At convergent boundaries, earthquakes can occur at different depths. Deep focus earthquakes happen along a subducted plate, while shallow focus earthquakes occur where one plate begins to be thrust under the other. Shallow focus earthquakes are more frequently observed than deeper ones, as depicted in the left diagram. The distribution of earthquakes at a convergent boundary is represented by red dots.

Continental shields, which are composed of ancient rocks, are flat and stable interiors of the continents. The majority of the stress resulting from tectonic movements is relieved through earthquakes at the boundaries of plates. Nevertheless, stress can also accumulate within the plate interiors. The old fault lines within these plates, which are weaker than the surrounding rocks, intersect each other across many continents. If the stress from recent plate movements becomes too great, these old fault lines can slip, leading to unexpected earthquakes. This poses a problem as many of these old fault lines are unknown and located far from the current plate boundaries.

The potential danger of earthquakes exists in many modern settlements, even if they are not located near current faults. The distribution of earthquakes within continental shields is still uncertain; scientists do not know if the same region within a tectonic plate will be affected. Inter-plate earthquakes have a relatively lower intensity compared to boundary earthquakes, and their occurrence is infrequent. The latest significant inter-plate earthquake occurred in Latur, India in 1993.

However,

earthquakes can occur in unexpected regions where there has been no previous history of earthquakes. They can also spread their energy further without losing as much due to the transmission properties of older hard rocks compared to deformed and broken younger rocks. This can result in more damage over a larger area. Earthquakes are frequent occurrences and can be caused by various factors within the Earth's interior.

The strength and frequency of earthquakes in a particular area depend on the type of area they occur in, as well as the cause of the earthquake. Today, we have a good understanding of how earthquakes are caused and can track their occurrences on a daily basis. This knowledge has greatly enhanced our understanding of earthquakes. However, one important question remains: when and where will the next earthquake strike? Despite the available technology, it is important to acknowledge that we are still far from being able to predict earthquakes accurately.

Bibliography

Understanding Earth 2nd edition by Frank Press and Raymond Siever. Microsoft Encarta Encyclopaedia 1998.