However, accurate recordings of earthquakes only began in the early 1900s, so it is too early to categorically state that this is the case.Most of the worlds earthquakes (90%, and 81% of the largest) take place in the 40,000-kilometre-long (25,000 mi), horseshoe-shaped zone called the circum-Pacific seismic belt, known as the Pacific Ring of Fire, which for the most part bounds the Pacific Plate. Massive earthquakes tend to occur along other plate boundaries too, such as along the Himalayan Mountains.With the rapid growth of mega-cities such as Mexico City, Tokyo and Tehran in areas of high seismic risk, some seismologists are warning that a single earthquake may claim the lives of up to three million people. Induced seismicity
While most earthquakes are caused by movement of the Earths tectonic plates, human activity can also produce earthquakes. Activities both above ground and below may change the stresses and strains on the crust, including building reservoirs, extracting resources such as coal or oil, and injecting fluids underground for waste disposal or fracking. Most of these earthquakes have small magnitudes. The 5.7 magnitude 2011 Oklahoma earthquake is thought to have been caused by disposing wastewater from oil production into injection wells, and studies point to the states oil industry as the cause of other earthquakes in the past century. A Columbia University paper suggested that the 8.0 magnitude 2008 Sichuan earthquake was induced by loading from the Zipingpu Dam, though the link has not been conclusively proved.
Hypocholesterolemia is the presence of abnormally low (hypo-) levels of cholesterol in the blood (-emia). A defect in the bodys production of cholesterol can lead to adverse consequences as well. Cholesterol is an essential component of mammalian cell membranes and is required to establish proper membrane permeability and fluidity. It is not clear if a lower than average cholesterol level is directly harmful; however, it is often encountered in particular illnesses. Presentation
Role in disease
With the increased use of medication to suppress cholesterol, some have expressed concern that lowering cholesterol levels excessively will itself cause disease. Specific disease entities
Demographic studies suggest that cholesterol levels form a U-shape curve when plotted against mortality; this suggests that low cholesterol is associated with increased mortality, mainly due to depression, cancer, hemorrhagic stroke, aortic dissection and respiratory diseases. It is possible that whatever causes the low cholesterol level also causes mortality, and that the low cholesterol is simply a marker of poor health.Links with depression have been supported by studies. In contrast, no evidence was found for a link with hemorrhagic stroke (although higher cholesterol levels conferred a relative protection), and neither did statin drugs worsen the risk.The Heart Protection Study found no increase in either respiratory disease or neuropsychiatric illness in a large trial population taking a statin drug. Elderly
In the elderly, low cholesterol may confer a health risk that may not be offset by the beneficial effects of cholesterol lowering. Similarly, for elderly patients admitted to hospital, low cholesterol may predict short-term mortality.