| On Sunday, the state of Hawaii was shook by a very strong earthquake. Residents were jolted from their beds and a landslide ended up blocking a major highway. Many guests in hotels and patients in hospitals had to be evacuated. The aftershocks kept Hawaii and its residents on edge. Linda Lingle, the governor of Hawaii, issued a disaster declaration for her state. She remarked on the damage sustained by roads and buildings. As of press time, there were not reports of any fatalities. Several minor injuries were reported in the aftermath of the earthquake. The earthquake actually struck at 7:07 a.m. local time. It struck 10 miles north of Kailua Kona, which is located on the west coast of the Big Island, the island of Hawaii itself. The earthquake did prompt fears of a tsunami, which did not occur. As many as 3,000 people were evacuated from hotels as a result of the earthquake. Some hotels were damaged. The last earthquake this strong occurred in Hawaii some 20 years ago. A 6.1 magnitude earthquake, not as strong as Sunday's 6.6. earthquake, occurred in 1989.
Processes, occurring during powerful earthquakes:
Earthquakes start with a breaking up and shift of mountain rocks in any place in the depths of the Earth. This place is called the seismic centre or hypocentre. Generally, its depth is not more than 100 km but sometimes can reach up to 700 km. According to depth, seismic centers are classified as : normal - 70 - 80 km, intermediate - 80 - 300 km, deep -> 300 km. Sometimes, the seismic centre can be on the surface of the Earth. In such cases, if an earthquake is powerful, bridges, roads, houses and other structures are damaged and destructed.
The spread of tsunami waves in the Pacific ocean caused the earthquake in Japan (2011).
The part of the Earth, within the limits of which on the surface, over the seismic center, the force of underground tremors reach maximum value, is called the epicenter.
In certain cases, the layers of the earth located along the sides of the rupture, move towards each other. In other cases, the earth on one side of the rupture lowers, forming faults. Waterfalls appear in places, where they intersect riverbeds. Arches of underground caves crack and collapse. After the earthquake, huge sections of earth lower and get flooded with water. Underground tremors displace loose upper soil layers from slopes forming rockslides and landslides. In 1906, a deep crack was formed on the surface during the earthquake in California It stretched up to 450 kilometers.
Underwater earthquakes are reasons for tsunamis, long waves produced by the powerful action on the entire thickness of water in the ocean, during which there is sudden shift (rise or fall) of a section of the sea floor. Tsunamis are formed during an earthquake of any intensity but major tsunamis arise due to powerful earthquakes (more than 7 points).
It is understood that, the sudden displacement of large sections of earth near the epicenter is accompanied by an impact of enormous force. In a year, people on Earth feel about 10 000 earthquakes. Among them, approximately 100 happen to be destructive
Other types of earthquakes:
Volcanic earthquakes:
Volcanic earthquakes are a type of earthquake, in which an earthquake occurs as a result of high stress in a volcano subsoils. The reason for such earthquakes - lava, volcanic gas. Earthquakes of this type are weak but continue for longer periods, for weeks and months together. Nevertheless, the earthquake does not pose danger to populations.
Technogeneous earthquakes:
Recently, information has appeared that earthquakes can be caused by man's activities. Like, for instance, the increase in tectonic activity is observed on constructing large water reservoirs in flood-prone areas, thus increasing the frequency of earthquakes and their magnitude. This is associated with the fact that, a mass of water, accumulated in water reservoirs, with its own weight, increases the pressure in the rocks, and the infiltration of water lowers the strength of the rocks. Similar phenomena take place during oil and gas extraction (a series of earthquakes with a magnitude of up to 5 occurred in the Romashkino oil fields in Tatarstan) and excavation of large quantities of rocks from mines, quarries and during construction of big cities using imported materials.
Landslide earthquakes:
Earthquakes can also occur due to avalanches and landslides. Such earthquakes are called landslide earthquakes, as they are local in nature and are very weak.
Earthquakes of artificial nature:
An earthquake can be invoked artificially: for example, an explosion using a large quantity of explosives or an underground nuclear explosion (tectonic weapons). Such earthquakes depend on a quantity of explosive substance. For example, during nuclear tests by the Democratic People's Republic of Korea in 2006, a moderate earthquake was registered in many countries. |
[ Hawaii was shaken by a strong earthquake this Sunday. Even though there were no victims, the last Hawaiian earthquake this strong (magnitude of 6.5) struck more than 20 years ago. ] 
