Posts Tagged ‘Chile’

Chile, Haiti Earthquakes Point to Need for Quake-Proof Buildings

Monday, March 22nd, 2010

Civil engineers can design buildings that don’t collapse when the earth’s tectonic plates shift.  Two massive earthquakes in a single month – an 8.8 trembler in Chile and a 7.0 quake in Haiti – have raised the question of whether engineers can design buildings that don’t crumble when the earth’s tectonic plates crash against one another. Although the simple answer is that the technology exists to make buildings almost earthquake-proof, the cost of rebuilding sprawling cities that are hundreds of years old would be prohibitively expensive.

“Most disasters are created by human beings.  It’s how we build and where we build that creates the hazard, the disaster,” said Michael Armstrong, senior vice president of the International Code Council, a non-profit organization that develops building codes.  “Earthquakes, hurricanes, fires, floods are going to occur, but there are ways in terms of where we build and how we build that can reduce the impact.”

Essentially, the technology that prevents buildings from collapsing during earthquakes works by making buildings stronger or more flexible so they sway and slide rather than crumble.  For nearly three decades, engineers have constructed skyscrapers that float on systems of ball bearings, springs and padded cylinders.  Because these buildings don’t sit directly on the earth, they are protected from some earthquakes.  During a major earthquake they may sway a few feet in synch with the tremor.

Mehmet Celebi, a senior research civil engineer with the U.S. Geological Survey, pointed to a striking example where buildings constructed with base isolation performed exceptionally in earthquakes while others did not.  Base isolation is a collection of structural elements which should substantially decouple a superstructure from its substructure resting on a shaking ground, thus protecting a building‘s structural integrity.  He cited a University of Southern California hospital in Los Angeles that came through the 1994 Northridge earthquake with no damage.  A nearby hospital that did not incorporate the same technology suffered significant damage.

Chilean Earthquake Shortened Day, Knocked Earth Off Its Axis

Tuesday, March 9th, 2010

Chile’s 8.8 magnitude earthquake shortened the day by 1.26 microseconds, knocked earth three inches off its axis.  The 8.8 magnitude Chilean earthquake was so strong that it literally knocked the earth off its axis – permanently. Richard Gross, a research scientist at NASA’s Jet Propulsion Lab, calculated that the earth’s rotation changed so that the length of our day is now roughly 1.26 microseconds shorter.  A microsecond is equivalent to one millionth of a second.  The Chilean quake also shifted earth’s figure axis (the axis on which our planet’s mass is balanced) by three inches.

By contrast, the 9.1 magnitude 2004 Sumatran earthquake shifted the earth’s axis by 2.76 inches and made the day shorter by 6.8 microseconds.  The larger shift in the earth’s axis as the result of a slightly smaller earthquake is because the Chilean trembler occurred in the earth’s mid-latitudes.  The fault responsible for Chile’s quake also cuts more deeply into the earth and at a steeper angle than in Sumatra.  Haiti’s 7.0 January earthquake, which occurred close to the surface, had no impact on the earth’s rotation.