The topic of the current paper is the Northridge earthquake. In fact, it is highly important to study this topic, as the California area is considered one of the highly seismic in the country. A great number of earthquakes are recorded every year. Some of them are harmless, while some earthquakes bring real damage to many cities. Actually, the Northridge earthquake belongs to the group of destructive earthquakes. Despite the fact that the magnitude of earthquake was only at the level of 6.7 on the Richter scale, the consequences of the earthquake were catastrophic. Many experts associate it with the fact that the construction of the buildings was not suitable for the area with such a high seismic activity. In such a way, it is significant to examine the case of the Northridge earthquake in order to prevent similar cases in the future.
Keywords: earthquake, California, Northridge, fault, shocks, buildings, damage
1994 Northridge Earthquake
In fact, California is famous for the seismic activity. However, the XX century is considered to be extremely destructive for this geographic area. Northridge is located 30 miles from Los Angeles in the zone of a small fault that extends from San Andreas to the ocean. One of the most famous geological phenomena of the planet – the San Andreas Fault – is located along the Pacific coast in California. Actually, this horizontal fracture is rather long and it forms the boundary between the Pacific and North American tectonic plates. Two tectonic plates are continuously sliding on the side surface of each other at a speed of about 5 cm per year. Many small faults, which are connected to the San Andreas Fault, cross the district. Thus, a great number of earthquakes in this area happen every year. In Northridge, a terrible earthquake happened in 1994 that was the most powerful in the past 50 years. Despite the fact that the earthquake was rather short, it was extremely destructive. The earthquake destroyed many buildings and claimed the lives of several dozens of people. The purpose of the paper is to study the history of the Northridge earthquake and to examine the amount of damage it brought.
History of the Earthquake
California is well-known for the seismic activity. In fact, earthquakes usually bring much damage to the region. The book Earthquake Engineering for Structural Design states that “earthquakes represent the largest potential source of causalities and damage for inhabited areas due to natural hazard” (Gioncu & Mazzolani, 2010, p. 1). In California, from 10 to 20 earthquakes are happening daily (Stein & Mazzotti, 2007). Every year, more than 20 thousand cases of shocks are recorded in this area (Stein & Mazzotti, 2007). Fortunately, not all of the earthquakes reach the destructive power, as they are softened by the oceanic and terrestrial masses. Most of them originate in the San Andreas Fault, which has a length of 1,300 km and a depth of 15 km (Stein & Mazzotti, 2007). Thus, the San Andreas Fault crosses almost the whole territory of California and is considered to be the most dangerous fault of the planet. The geologists are confident that the southern part of the San Andreas Fault causes large shocks every 150 years (Stein & Mazzotti, 2007). The earthquakes that originate in this area can bulldoze the entire town. Therefore, the children in California are accustomed to the alarms for instruction, as the constant threat of earthquakes is an integral part of their everyday life and studies at school. However, the seismologists have discovered a danger that is more serious. In addition to the great San Andreas Fault in Southern California, there are more than 150 big faults (Stein & Mazzotti, 2007). The fault that is located at a depth of 3 km is even more dangerous than the San Andreas Fault because it is located right near Los Angeles (Stein & Mazzotti, 2007). The dangerous fault, the Puente Hills, has been discovered only recently. Actually, two giant platforms constantly rub against each other and the pressure between them grows gradually. In such a way, it can represent a great danger for this territory.
The most famous US earthquake of the XX century is still considered to be the earthquake in San Francisco, California that happened in 1906 (Stein & Mazzotti, 2007). Actually, the earthquake was 45 times stronger than the earthquake that devastated Northridge (Stein & Mazzotti, 2007). The tremors caused fires and claimed 3,000 lives of people (Stein & Mazzotti, 2007). After that devastating earthquake, four other earthquakes occurred in the state – in 1971, 1983, 1989, and 1994 (Stein & Mazzotti, 2007). California is certainly the most seismic region of the United States.
The infamous Northridge earthquake in Los Angeles, CA happened on January 17, 1994 (Olshansky, Johnson, & Topping, 2006). The first tremor was registered at 4:31 am (Stein & Mazzotti, 2007). The magnitude was far from impressive – 6.7 on the Richter scale (Olshansky, Johnson, & Topping, 2006). However, the destructive effect produced by an earthquake was truly devastating. The seismic blow fell on the San Fernando Valley, just 20 miles to the northeast of downtown Los Angeles (Olshansky, Johnson, & Topping, 2006). At first, San Fernando was considered the epicenter of the disaster. Although, Northridge was defined as the epicenter of the earthquake later; thus, the earthquake took the name of the town. However, the calculations provided the following geographical coordinates of the epicenter a week later: 32 degrees 12 minutes 47 seconds north latitude, 118 degrees 32 minutes 13 seconds west longitude (Veitch, 2008). In fact, this point is located in the town of Reseda.
The Degree of Destruction
The territory located at a distance of 85 miles from the epicenter was subjected to the destruction of the earthquake. The Simi Valley, the city of Santa Monica, and the San FranciscoValley suffered the most (Fig. 1). In fact, the earthquake seriously damaged Santa Monica, as the central hospital and hundreds of houses were destroyed. Moreover, a famous stadium in Anaheim, which was located 50 miles to the south from the epicenter, was partially destructed (Bolin & Stanford, 2006). Thus, a great territory suffered from the earthquake.
The infrastructure of the area was completely destroyed. The shocks that lasted up to 20 seconds destroyed 10 road bridges and put out of action three major highways. In addition, the roads were destroyed within a radius of 20 miles from the epicenter (Bolin & Stanford, 2006). The destructive power of nature was evident in the devastated areas of the expressways (Fig. 2). The earthquake interrupted the daily trip to work of approximately one million inhabitants of Los Angeles. Thus, the Northridge earthquake represented the most serious challenge to the California Transportation Department in a 100-year history (Bolin & Stanford, 2006). Moreover, the department spent two years to restore all the blasted motor highways. Despite the difficulties and costs associated with constant works, most of the residents of Los Angeles approved the efforts California Transportation Department dedicated to the highway reconstruction. The office of the governor on planning and research issued a report, which stated that motorway restoration cost amounted to more than $ 1 million to the local economy every day (Bolin & Stanford, 2006). In such a way, the consequences of the earthquake were felt for several years.
A series of office buildings, hotels, residential buildings, and hospitals were completely destroyed. The book Soil Stress-Strain Behavior notes that “although tall buildings are relatively few in the Los Angeles area, more than 150 buildings with welded steel moment resisting frames were significantly damaged during the earthquake” (Ling, Callisto, Leshchinsky, & Koseki, 2007, p. 939). Actually, the investigation found that at least one of the destroyed apartment buildings was built with the violation of specifications for construction in seismic areas such as California. However, it became clear that the processing was needed for the specifications, since they did not provide adequate protection for the buildings against the seismic factors. However, a part of the damage was caused not by the shocks but by the changes in relief and fire that followed them. According to various estimates, the Northridge earthquake cost from 20 to 30 billion dollars (Ling et al., 2007). Moreover, more than 20 thousand people became homeless. In addition, about 9000 people received injuries of different severity and 57 people died (Veitch, 2008). People died under the rubble of destroyed buildings and in cars on the highways. Actually, the earthquake happened on the national holiday of the birthday of Martin Luther King. Therefore, people were on their day off. However, more victims would suffer from the earthquake, if it occurred on a working day.
Actually, the earthquake caused landslides and fires. The combustions occurred frequently due to the destruction of the pipeline (Olshansky, Johnson, & Topping, 2006). The consequence of the earthquake represented the outbreak of respiratory infectious disease. Due to the Northridge earthquake, many central highways and railways were destroyed. In addition, the largest universities in the country, such as California State University, were closed (Olshansky, Johnson, & Topping, 2006). Moreover, Hollywood studios and record companies of the area were closed during some time. Several important basketball games were postponed. The Northridge earthquake brought down the television and radio broadcasting. In fact, e-mail message did not work for several days after the disaster. What is important, many insurance companies were forced to declare their bankruptcy (Olshansky, Johnson, & Topping, 2006). The consequences of the earthquake were so destructive that the restoration works lasted for the next few years.
The majority of earthquakes occur in the places of joints of plates that form the earth’s crust. The fact that the plates are constantly moving causes them to change shape and voltage (Stein & Mazzotti, 2007). If the voltage is greater than the resistance of the crust, a sudden shift of the earth’s crust happens and the energy and the appearance of seismic waves on the earth’s surface are released. The place, where the release of energy happens, is called the epicenter of the earthquake and a place on the earth, where the epicenter of the earthquake is located, is called the earthquake source point (Stein & Mazzotti, 2007). The amount of energy released on the point of focus of the earthquake is determined by the Richter magnitude scale (M) (Stein & Mazzotti, 2007). The earthquake with a magnitude of M4 is clearly felt in the epicenter. The earthquake of medium magnitudes of M5 and M6 can cause minor damage. However, the earthquake of M7 and M8 magnitudes can cause not only major damage to the buildings but also landslides and residual movement on the ground. If the building is located on a fault line, the collapse of the ground under the foundation can damage the building. The collapse of unstable slopes and loose soil leads to the destruction of the building. Most of the damage occurs due to the seismic waves that emanate from the epicenter of the earthquake. A strong movement of the earth leads to the motion of the building. When the foundation moves at the time of the earthquake, inertia force tries to keep the highest floors in place. If the movements are slow, then the building holds out. However, the earthquake quickly creates shocks. Generated during the earthquake, they depend on the mass of the building and on the received shocks (Stein & Mazzotti, 2007). If the mass of high-rise buildings is big, the shocks of the earthquake in the buildings will be high. At the same time, the large shocks of the earth can cause damage to large buildings. Thus, the earthquake affects the building depending on the nature of the motion of various structures of the building.
In fact, the Northridge earthquake reached almost 7 points. Despite this fact, it caused significant damages due to the improper construction of the buildings. Actually, no building can be completely resistant to earthquakes. The proper seismic design will allow minimizing the damage caused by earthquakes (Bolin & Stanford, 2006). The wooden frame constructions are ideal for the design of earthquake-prone zones due to their design characteristics such as reliability, ease, and flexibility. The ground moves during an earthquake (Bolin & Stanford, 2006). The transmission of the motion to the building is necessary to be performed in the same direction and, thus, the building and the ground should move in one direction. The destruction of the buildings occurs due to reverse forces that arise from such a movement and the materials used in the construction that do not withstand these forces.
The earthquake in Northridge presented that multi-storey buildings with a garage on the ground floor received the most damage (Ling et al., 2007). Such an experience provides a more in-depth and thorough development of the building codes and the standards for buildings to ensure that they could withstand the earthquake. In the report on operational qualities of wood-frame structures during the earthquake, it is emphasized that the structural elements of wood-frame houses received minimal damage from the earthquake (Ling et al., 2007). In such a way, it is possible to make a conclusion that wood-frame houses are the most suitable for the areas with high seismic activity.
After the Northridge earthquake, the state and the country authorities developed a program to build seismosafe houses and buildings. Actually, the distribution of the procedures on seismic safety and the control of elimination or reconstruction of potentially dangerous buildings and the ones on the verge of destruction happened in the area (Ling et al., 2007). The authorities intend to take into account the recommendations of the specialists on the condition of the ground in the construction of the future buildings in cities; the authorities also create houses from the materials that will be less damaging for the people living in them in case of the possible earthquakes (Ling et al., 2007). The book The Northridge Earthquake notes that “the professional earthquake community reasons that by knowing the objective risks of future earthquakes, new earthquake resistant building standards and seismically informed land use planning can be rigorously implemented so that future disaster is avoid” (Bolin & Stanford, 2006, p. 16). Thus, the construction of buildings from environmentally sustainable and durable materials will help to save dozens of lives during the natural disasters in the future.
In fact, the earthquakes are not rare in California. Such a situation is associated with the existence of the famous San Andreas Fault and other faults that represent a great danger to this area. The Northridge earthquake happened on January 17, 1994 near Los Angeles, California. The shocks lasted for nearly 20 seconds. Despite the fact that its strength was at the level of 6.7 points, the earthquake had extremely devastating consequences for the area. A great number of people were wounded and killed. Moreover, the damage from the earthquake reached several dozen of billions. The destruction was in a radius of more than a hundred kilometers from the epicenter of the earthquakes shocks.