Although more times than not earthquakes are tectonic, they can also occur in volcanic regions.
Although many people seem to think that the only earthquakes that take place are those which can be felt, that belief is completely false. Instead, large numbers of earthquakes take place daily across the world, but the majority of these can only be felt by seismometers and cannot be felt by the person and cause no structural damage of any sort. The strength and damage caused by an earthquake can vary dramatically, depending on the strength of the earthquake. Smaller earthquakes may go completely unnoticed, while larger earthquakes can cause serious destruction and massive loss of life. In fact, most of the larger earthquakes are then followed by smaller ones - these are otherwise known as foreshocks or aftershocks; foreshocks being smaller earthquakes which precede the larger earthquake, and aftershocks being those which procede it.
The first method of recording earthquakes was through of certain scales called intensity scales. The United States, Japan, and Europe each have their own form of scales. However the problem with all of these scales is that they are often a poor measure for the relative size of different events in different places. Seismologists now favor a measure called the seismic movement, which relates to the concept of moment in physics, to measure the size of a seismic source.
The 1995 Great Hanshin Earthquake - which is commonly referred to as the Kobe earthquake due to the fact that it took place near Kobe, one of Japan's largest and most populated cities - was one of the most devastating earthquakes to ever hit Japan. Although over ten years have passed now since this earthquake hit, it is still considered to be one of the most disastrous ever to hit Japan since the Great Kanto earthquake of 1923, and will not soon be forgotten. In due to this earthquake, more than 5,500 people were killed, with more than 26,000 left injured. The total economic loss was estimated as being approximately $200 billion USD.
During this earthquake, it was recorded that the ground moved 7 inches in horizontal shaking, and 4 inches in the vertical direction, and the earthquake itself is actually still active, with 716 aftershocks recorded by 10 AM as of January 18, 1996, 74 of these could be felt by the human body, and 14 of these occurred on the 18th. The epicenter of the earthquake was 20km underneath the island of Awaji, across a strait from Kobe.
With a magnitude of 6.9 (Mw) and a duration of roughly 20 seconds, in regards to the structural damage caused by the earthquake, there were: 144,032 buildings destroyed by ground shaking, 7,456 buildings destroyed by fire, 82,091 collapsed buildings, and 86,043 severely damaged buildings. All Kobe ports were shut down to international shipping, there was substantial damage to containing loader piers, and all access to Kobe via highway and railway were blocked.
The Kobe earthquake struck early in the morning without any warning, taking the city completely by surprise. It was due to the city of Kobe's high population density and linear layout, that there was such substantial damage and trauma caused; infrastructure networks were made much less redundant because of this, and this was a key factor in the significant structural