Monday, January 25, 2010

Haitian Fault






One thing about major active faults is that there are not too many of them. In fact they are rather uncommon and easily detected if you have your eyes open.  If faults are active, the ground bends and warps forming a scarred landscape.  It is easily recognized around LA or San Francisco.

There are also better hidden ones out in flat country that way more tricky to spot or well eroded old ones that sometimes come back to life.

However, the majority of quakes come from the same well known faults as we have just seen in Haiti.

The first problem is that people build along them.  This can not be properly avoided because a decent exclusion zone would be fifty miles to either side of the fault.  Yet San Francisco has shown that building codes can sharply curtail damage and death rates.

Their last quake was the same magnitude as the Haitian quake and their death toll was 68.  That starts been within an acceptable range for that level of disturbance.

The absolute key to it all are building codes that minimize the collapse threat.  That is what has killed possibly 200,000 in Haiti.  We see pictures of piles of concrete and almost no rebar.  Those buildings actually crumbled.

The first rule is to stop building unreinforced concrete structures at all.  Even better, adopt wood frame construction for housing up to three stories.  A quake will still tear them apart but they are fighting it all the way.  In Kyoto a few western build structure were noticeably still standing.

I can go further than that.  I can produce stress skinned panels that have perhaps half the weight and twice the strength for about the same end cost after construction.  It has not been made to happen yet, but it is feasible and is the future of global housing for that and superior energy retention and ease of construction.

Nothing is ever bullet proof but Haiti’s quake was survivable.  There was little ground damage suggesting foundations could survive.  Once the building is able to avoid collapse, the remaining threat is land movement and that is local and rare enough to ignore.

Haiti would be well served to switch totally to termite treated wood frame housing even if stress skin is not available. 

My point remains.  It is possible to build out a completely new Haiti using stress skin panel construction presently unavailable, at similar cost to other options, able to withstand a magnitude 7 quake and withstand a level 4 hurricane and possibly much more with negligible loss to human life.  A friend put several years of his life into perfecting the necessary art and I spent many months confirming and analyzing the economic model to an optimum solution.

Fault Responsible For Haiti Quake Slices Island's Topography

by Staff Writers  Washington DC (SPX) Jan 18, 2010



The sharp diagonal line exactly at the image center is the Enriquillo fault. Port-au-Prince is immediately to the left (north) at the mountain front and shoreline.


A magnitude 7.0 earthquake occurred on January 12, 2010, at Port-au-Prince, Haiti, with major impact to the region and its citizens. This perspective view of the pre-quake topography of the area clearly shows the fault that is apparently responsible for the earthquake as a prominent linear landform immediately adjacent to the city.



Elevation is color coded from dark green at low elevations to white at high elevations, and the topography is shaded with illumination from the left. The topography in this image is exaggerated by a factor of two.


The sharp diagonal line exactly at the image center is the Enriquillo fault. Port-au-Prince is immediately to the left (north) at the mountain front and shoreline.


The Enriquillo fault generally moves left-laterally (horizontally, with features across the fault shifting to the left when the fault breaks in an earthquake), but vertical movements occur along the fault where irregularities in the fault line cause local compression or extension of the earth.


Meanwhile, movements of the topography at the Earth's surface can falsely appear to be vertical where mountain slopes are cut and misaligned by horizontal shifts of the fault.


Additionally, differing erosion rates on the two sides of the fault, due to the juxtapositioning of differing rock types by the fault, can give the appearance of vertical offsets of the current topographic surface. All of these real and apparent horizontal and vertical offsets of the topographic surface may (and likely do) occur here, making the fault easily observed in the topographic data.


The elevation data used in this image were produced by the Shuttle RadarTopography Mission (SRTM), flown aboard Space Shuttle Endeavour in February 2000. SRTM acquired elevation measurements for nearly all of Earth's landmass between 60 degrees North and 56 degrees South latitudes.


For many areas of the world, SRTM data provide the first detailed three dimensional observation of landforms at regional scales.


The mission was a cooperative project between the National Aeronautics and Space Administration (NASA), the National Geospatial-Intelligence Agency (NGA) of the U.S. Department of Defense (DOD), and the German and Italian space agencies. It was managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif., for NASA'sScience Mission Directorate, Washington, D.C.


View Width: One degree latitude (111 kilometers, or 69 miles)
View Distance: Five degrees longitude (525 kilometers, or 325 miles)
Location: 18 to 19 degrees North latitude, 70 to 75 degrees West longitude
Orientation: View east, 5 degrees below horizontal
SRTM Data Acquired: February 2000


Haiti Quake Occurred In Complex Active Seismic Region

by Staff Writers
Woods Hole MA (SPX) Jan 21, 2010


The magnitude 7.0 earthquake that triggered disastrous destruction and mounting death tolls in Haiti this week occurred in a highly complex tangle of tectonic faults near the intersection of the Caribbean and North American crustal plates, according to a quake expert at the Woods Hole Oceanographic Institution (WHOI) who has studied faults in the region and throughout the world.



Jian Lin, a WHOI senior scientist in geology and geophysics, said that even though the quake was "large but not huge," there were three factors that made it particularly devastating: First, it was centered just 10 miles southwest of the capital city, Port au Prince; second, the quake was shallow-only about 10-15 kilometers below the land's surface; third, and more importantly, many homes and buildings in the economically poor country were not built to withstand such a force and collapsed or crumbled.


All of these circumstances made the Jan. 12 earthquake a "worst-case scenario," Lin said. Preliminary estimates of the death toll ranged from thousands to hundreds of thousands. "It should be a wake-up call for the entire Caribbean," Lin said.


The quake struck on a 50-60-km stretch of the more than 500-km-long Enriquillo-Plantain Garden Fault, which runs generally east-west through Haiti, to the Dominican Republic to the east and Jamaica to the west.


It is a "strike-slip" fault, according to the U.S. Geological Survey, meaning the plates on either side of the fault line were sliding in opposite directions. In this case, the Caribbean Plate south of the fault line was sliding east and the smaller Gonvave Platelet north of the fault was sliding west.


But most of the time, the earth's plates do not slide smoothly past one another. They stick in one spot for perhaps years or hundreds of years, until enough pressure builds along the fault and the landmasses suddenly jerk forward to relieve the pressure, releasing massive amounts of energy throughout the surrounding area. A similar, more familiar, scenario exists along California's San Andreas Fault.


Such seismic areas "accumulate stresses all the time," says Lin, who has extensively studied a nearby, major fault , the Septentrional Fault, which runs east-west at the northern side of the Hispaniola island that makes up Haiti and Dominican Republic. In 1946, an 8.1 magnitude quake, more than 30 times more powerful than this week's quake, struck near the northeastern corner of the Hispaniola.


Compounding the problem, he says, is that in addition to the Caribbean and North American plates, , a wide zone between the two plates is made up of a patchwork of smaller "block" plates, or "platelets"-such as the Gonvave Platelet-that make it difficult to assess the forces in the region and how they interact with one another. "If you live in adjacent areas, such as the Dominican Republic, Jamaica and Puerto Rico, you are surrounded by faults."


Residents of such areas, Lin says, should focus on ways to save their lives and the lives of their families in the event of an earthquake. "The answer lies in basic earthquake education," he says.


Those who can afford it should strengthen the construction and stability of their houses and buildings, he says. But in a place like Haiti, where even the Presidential Palace suffered severe damage, there may be more realistic solutions.


Some residents of earthquake zones know that after the quake's faster, but smaller, primary, or "p" wave hits, there is usually a few-second-to-one-minute wait until a larger, more powerful surface, or "s" wave strikes, Lin says. P waves come first but have smaller amplitudes and are less destructive; S waves, though slower, are larger in amplitude and, hence, more destructive.


"At least make sure you build a strong table somewhere in your house and school," said Lin. When a quake comes, "duck quickly under that table."


Lin said the Haiti quake did not trigger an extreme ocean wave such as a Tsunami, partly because it was large but not huge and was centered under land rather than the sea.


The geologist says that aftershocks, some of them significant, can be expected in the coming days, weeks, months, years, "even tens of years." But now that the stress has been relieved along that 50-60-km portion of the Enriquillo-Plantain Garden Fault, Lin says this particular fault patch should not experience another quake of equal or greater magnitude for perhaps 100 years.


However, the other nine-tenths of that fault and the myriad networks of faults throughout the Caribbean are, definitely, "active."


"A lot of people," Lin says, "forget [earthquakes] quickly and do not take the words of geologists seriously. But if your house is close to an active fault, it is best that you do not forget where you live."


The Woods Hole Oceanographic Institution is a private, independent organization in Falmouth, Mass., dedicated to marine research, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the oceans and their interaction with the Earth as a whole, and to communicate a basic understanding of the oceans' role in the 

2 comments:

Pbody said...

There are many building technologies that are available for reconstruction of Haiti. Typically, the Caribbean used reinforced concrete block due to hurricanes. Wood construction or stressed skin construction does not work there. What is the point of this article? To demonstrate what you do not know?

arclein said...

concrete is used as a hurricane resistant system, but the failing is that no one reinforces it enough. I am sure that the roofs also do poorly in a severe hurricane.

in the event, the same size of quake has hit California with a handful of casualties. The only plausible reason is lack of steel.

Stress skin panels properly made are not to my knowledge been produced yet. We were able to solve the technical problems and cost issues but were likely a decade or two early.

Using stress skin panels it is possible to produce a shell that is twice as strong as best practice wood frame and completely and continuously bonded on all edges or possible points of failure.

Also important was that the weight could be reduced about forty percent less than that of conventional wood frame. The core product was in fact cleared with those specifications with CMHC in Canada(a two mill. task by itself).

The weight and brittleness of concrete caused spectacular failure in Haiti. I do not know what building codes existed there, but it looks like badly secured post and pillar work unable to stand up to much movement at all.

I also see far too little steel in the piles of rubble.

Earthquake resistance is a function of good design, weight and strength.

Hurricane resistance is mostly about sheer strength and strong bonds to keep things from been torn apart.

The first thing that needs to go for earthquake resistance is weight and of course, that is the problem with a lot of traditional building.

Concrete by itself provides often unnecessary weight and strength mostly in one direction which is why it is seen to crumble and crack under violent shaking.

As noted ordinary wood frame stood up in Kyoto while whole neighborhoods of traditional post and beam collapsed around them.

The key to using wood based products is insect treatment and manufactured panel product to prevent inevitable substitution.