Mapping an effective earthquake response

The most powerful earthquake ever observed on the eastern coast of the U.S. struck in the Palmetto state, with an epicenter near Summerville, just north of Charleston. Given that it happened more than a hundred years ago, in 1886, and that South Carolina is hardly Southern Cal when it comes to periodic earthquake-induced renovations, the event might seem relegated solely to history lessons.

Unfortunately, that’s not how it goes with earthquakes. You don’t need to look any further than Erin Derrick’s seismology studies at the University of South Carolina to understand that.

Her work is bringing clearer focus to the fault lines under the Lowcountry. With the distinct possibility that a similar magnitude-7 temblor might hit the now heavily populated region, her research is a crucial contribution to the effort to develop an effective emergency response plan for the area.

“Out in California, in Washington, you have plates either coming together or sliding past each other,” says Derrick, a doctoral student in geology professor Jim Knapp’s laboratory. “That’s why you get so many large earthquakes out there.

“But here, we’re not doing much tectonically. The nearest plate boundary is thousands of miles away. So why are we having earthquakes? It’s actually an amazing story that dates back over 200 million years.”

South Carolina’s seismic activity is different from California’s because it’s the result of continental plates spreading apart rather than sliding or colliding. More than 200 million years ago, the continent of Africa was conjoined with North and South America. What’s now the Sahara desert was adjacent to what’s now Charleston, says Derrick.

Africa and the Americas began to separate in the Mesozoic era, creating the Atlantic Ocean and expanding it to its current size over tens of millions of years. The tremendous forces involved over the course of that separation produced faults throughout a wide expanse of area in the Southeast, called the South Georgia Rift Basin. It extends from South Carolina down into Alabama, Georgia and parts of northern Florida.

Knapp and his students and post-doctoral fellows have been studying that basin since his arrival at South Carolina in 1998. Derrick is building on their work and focusing specifically on a portion of the Charleston area, or what is technically termed the Middleton Place Summerville Seismic Zone.

That area has been the location of a series of small (magnitude 4 or less) earthquakes recorded since precise instruments were installed there in the 1970s. Supported in part by a SPARC graduate fellowship from the office of research, Derrick is completing an analysis of the data, damage records of the 1886 quake and seismic reflection and refraction experiments that has led to a new interpretation of the fault lines in the area.

In particular, Derrick is proposing the location and structure of a new fault, the Lincolnville fault. “It’s actually quite important because it runs underneath, or along, Interstate 26, which is the major transportation artery in and out of Charleston,” she says. “If a major earthquake were to hit that area, it’s essential for public safety to make transportation plans that take that into account.”

For Derrick, being able to make a concrete contribution to emergency preparedness is gratifying. “I was a physics and math major as an undergrad,” the Florida native says of her time at Hillsdale College in Michigan. “I decided I wanted to do something a little more practical, more hands-on and more directly applicable to society. That’s how I ended up studying earthquakes and seismology.”

And she’s more than pleased with her choice of working with Knapp in South Carolina's department of earth and ocean sciences.

“He’s been a great adviser. I’ve learned a lot from him,” she says. “He’s really helpful to get us where we need to be, to make us into scientists. It’s having the independence to develop but the guidance at the same time – that’s been really great.”

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