15 February 2010

Insight needed from civil and earthquake engineers

Posted by Michael McFadden

As D.C. endeavored to dig itself out following record-breaking snowfall, AGU headquarters still managed to push out Eos, its weekly newspaper.  In the 9 Feb issue was a new type of article for Eos–a news round table. In this particular article, called “In the Aftermath of Haiti’s Earthquake: A Discussion of Lessons Learned,” senior writer Randy Showstack interviewed three noted seismologists for their perspectives on what the earthquake means for science and for efforts towards disaster preparedness.

These scientists are:

Paul Mann, a senior research scientist with the Institute for Geophysics at the University of Texas at Austin. Mann recently returned from Haiti where he worked on a rupture survey.

Glen Mattioli, a professor of geosciences at the University of Arkansas, Fayetteville. Mattioli was part of a team conducting a Global Positioning System (GPS) survey of Haiti to measure ground deformation following the earthquake. Read the team’s blog.A collapsed school in Port- au- Prince, Haiti.

Carol Prentice, a seismologist with the U.S. Geological Survey’s Earthquake Hazards Team. Prentice has conducted paleoseismic research on the active faults in the Caribbean region since 1991.

I was particularly struck by issues raised that need more insight from the earthquake engineering community. Please read below and comment if you can shed light on some of these issues!

Q: What can science learn from the earthquake that shook Haiti on 12 January 2010?

Mattioli: …Geological observations will be used to determine whether the fault rupture propagated to the surface. Such information provides additional constraints on the geometry and slip of the event. Early reconnaissance and mapping by Roger Bilham (University of Colorado, Boulder) indicate that there is little evidence of surface rupture, although there are quite a bit of surface fracturing and some areas of significant uplift. Reconciling the geological and geomorphological observations with geodetic and seismic data will help us better understand why some shallow strike- slip events of approximately Mw 7 rupture to the free surface while others do not. It is not clear at this time why this is the case…

Aftershocks and preliminary Coulomb stress transfer models suggest that increased stress may exist in the region to the west of the 12 January main shock. Given that the geometry of the fault and the finite slip are still not well constrained, these models remain somewhat uncertain. We hope that the measurements made by our postseismic response team will help in this critical area. Obviously, already weakened structures are highly vulnerable, but these issues are better left to the earthquake engineering community to evaluate…

Prentice: …Through detailed studies of the Haitian earthquake, including its aftershocks, its effect on positions of geodetic stations, tectonic surface deformation, and secondary effects such as landslides and liquefaction, we will learn a great deal about the Enriquillo– Plantain Garden fault (EPGF) and related seismogenic structures…Additionally, we will learn about the soil conditions in Port- au- Prince that contributed to the terrible disaster…

Mann: …For those of us working in these areas, this is truly “urban geology” that contrasts with the “natural geology” that originally attracted many of us to the geosciences. Our study areas include all of those areas most affected by human habitation in the broad belts of people that surround large cities in developing countries: rambling neighborhoods of temporary houses ranging from cinderblock to tents, community gardens, abandoned factories, large landfills, and harbors ringed by cement plants, dock facilities, utility plants, and filled with both modern freighters at anchor and rusty hulks protruding at the surface. As population grows on these small islands in the coming decades, the entire land area will become blanketed by this dense urban “footprint” of humankind. But the science payoff for “urban geology” is crucial because that knowledge base will help protect the lives of millions of people crammed into and around these large population centers…

The quotes above raise several questions regarding civil and earthquake engineering. Can structures in Haiti be retrofitted or need the majority be completely rebuilt? Are studies being done to assess what buildings remained standing and why? I’ve spoken to some civil engineers and I wonder: Can structures be built to withstand liquifaction, and if so are building costs for even basic safeguards for this prohibitively expensive? Marginalized communities living in shantytowns are a fact of life in many seismically prone third-world urban centers. Can structures be built cheaply to withstand seismic hazards, and do these structures have a lower level of shaking tolerance compared to more formal buildings?

Let us know!

–Mohi Kumar, AGU Science Writer