Natural Disasters: Earthquakes

The Pacific Ring of Fire (or sometimes just the Ring of Fire) is an area where large numbers of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean. In a 40,000 km (25,000 mi) horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movements. The Ring of Fire has 452 volcanoes and is home to over 75% of the world's active and dormant volcanoes.^[1] It is sometimes called the circum-Pacific belt or the circum-Pacific seismic belt. [Wikipedia]

See also USGS map http://pubs.usgs.gov/gip/dynamic/fire.html

Before electronics allowed recordings of large earthquakes, scientists built large spring-pendulum seismometers in an attempt to record the long-period motion produced by such quakes. The largest one weighed about 15 tons. There is a medium-sized one, three stories high, in Mexico City that is still in operation. [USGS]

Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude; in terms of energy, each whole number increase corresponds to an increase of about 31.6 times the amount of energy released, and each increase of 0.2 corresponds to a doubling of the energy released.

Central Virginia Seismic Zone

USGS

Earthquake liquefaction, ... is the process by which saturated, unconsolidated soil or sand is converted into a suspension during an earthquake. The effect on structures and buildings can be devastating, and is a major contributor to urban seismic risk.  [ScienceDaily]

In the Christchurch Earthquake "... sandy soil was shaken violently, causing water to rise through its pores. Scientists compared it to jumping on wet sand at the beach - it soon turns to a murky soup."  [nzherald.co.nz Feb. 23, 2011]

A sand volcano after the Christchurch earthquake. Photo / NZPA