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An earthquake of only 5.2 was announced to have demolished a village in Iran. It is widely known that a quake of 6 or 7 is required for structural damage. Each Richter is a ten fold increase in strength from the former.
Agence France-Presse, July 4, 2003 Moderate Earthquake in Northeast Iran, no Casualties Reported An earthquake measuring 5.2 on the Richter scale shook northeast Iran on Thursday evening but there were no reports of casualties, state television reported Friday. The quake was felt across the Torbat-e Jam region, in Khorassan province, damaging or destroying 170 homes in 15 villages. The local population was being housed in makeshift tents provided by the Iranian Red Crescent. Earthquakes are a frequent occurrence in Iran where 950 have been reported across the country since 1991, leaving a total of 17,600 dead and 53,300 injured, according to the official news agency IRNA.
Again a quake in Japan of 5.6 had major damage reported, which would have required a quake closer to Richter 7.
Strong Quake Jolts the Coast of Japan Saturday [July 26] three major quakes that hit another northern state, Miyagi, leaving at least 420 people injured and hundreds of homes damaged.
From a Canadian Civil Engineering site:
The table below briefly describes earthquake effects corresponding to various magnitude levels and also gives an estimated number of earthquakes of different magnitudes that happen in the world each year. It can be observed from this table that a large majority of earthquakes (900,000) are of magnitude 2.5 or less (very minor earthquakes, usually not felt). Great, catastrophic earthquakes (magnitude 8 or greater) happen once in 5 to 10 years.
Magnitude Earthquake Effects Estimated Number @Year 2.5 or less Usually not felt, but can be recorded by seismograph. 900,000 2.5 to 5.4 Often felt, but only causes minor damage. 30,000 5.5 to 6.0 Slight damage to buildings and other structures. 500 6.1 to 6.9 May cause a lot of damage in very populated areas. 100 7.0 to 7.9 Major earthquake. Serious damage. 20 8.0 or greater Great earthquake. Can totally destroy communities near the epicenter. One every 5 to 10 years