Shake, Rattle, and Tidal Roll–Understanding Ocean Quakes

Kasey Aderhold loves feeling the earth move beneath her feet. “Seismology seems like a field we should know more about than we do,” she said. A third year doctoral student in the geophysics department at Boston University she researches a type of earthquake that recently piqued the interest of seismologists around the world.

Kasey AderholdIn a large room in the basement of the College of Arts and Science, Kasey sits at a computer crunching data collected from seismometers placed strategically around the world. Her pink hair stands out from the gray walls and stuffy atmosphere of the lab. “I used to have a faux hawk in a bunch of different colors, everyone used to ask me if I was an artist and I was like, ‘No! I’m a scientist!” she said.

Kasey grew up in the small town of Homer, Alaska, which has a population of 7,000 people. She spent most of her childhood exploring the Alaskan wilderness with her older sister. “I grew up doing outdoor things like hiking and fishing,” she said. “I thought I was going to be a biologist or something like that.” She never imagined her life would be so intertwined with earthquakes.

Homer is a hotbed of seismic activity. Not far from the Denali fault line, the town is surrounded by mountains and a volcano. Kasey experienced her first earthquake when she was eight years-old. “The earthquake shook long enough for me and my sister to hide under our dinner table,” she said. “The cat hid under the chair.”

Ten years later, Kasey left Alaska for Depaw University in Indiana. She received a scholarship she couldn’t pass up and the idea of a new place excited her. “I didn’t know anyone in the state, so it seemed like a great place to find out what I wanted to do with myself,” she said. After completing her Bachelor’s degree in computer science, Kasey was looking for a change. She yearned for the outdoors, and decided she’d rather spend her time outside than in front of a computer screen. “The computer science department was excellent and I had fabulous instructors who really inspired me to try new things,” she said. “I suppose they inspired me too much because I jumped ship to Earth Science.” Although Kasey’s background in the sciences was limited, her knowledge of computer programming gained her accepted to a graduate program in Boston studying earthquakes with Seismologist Rachel Abercrombie, a professor at Boston University.

A pioneer in her field, Abercrombie was the first person to install a seismometer deep in the earth’s crust to get better readings from strike-slip earthquakes on land. The method is now standard practice in seismology. Her current focus is on strike-slip quakes that occur in oceans. The research doesn’t lend itself to field work, which was disappointing for Kasey, but she isn’t giving up. When she gets the chance, Kasey assists her fellow grad students in their field work, and this summer she has an internship installing seismometers in Arizona.

Within the last decade, the number of seismometers around the world has drastically increased, making studying oceanic strike-slip earthquakes possible. These earthquakes, previously ignored by seismologists, are being used to gain insight into the behavior of all kinds of earthquakes around the world. Kasey studies two ocean strike-slip quakes that occurred in 2005 and 2010 on reactivated fracture zones near the Sumatran subduction zone. She uses mathematical modeling to figure out how deep they ruptured and how much slip, the displacement of earth along the fault, occurred. “Knowing how deep, where and how much slip occurred on a fault tells us how big the earthquakes can be,” she said.

This research is important because of oceanic strike-slip earthquakes’ potential influence on earthquakes that cause tsunamis. No one can forget the magnitude 9.1 earthquake and accompanying tsunami that killed thousands of people on the northern coast of Sumatra the day after Christmas in 2004. Three days earlier, one of the largest oceanic strike-slip earthquakes ruptured in the same area. Seismologists are now trying to determine if the strike-slip earthquake triggered the one that caused the tsunami, which could help them forecast devastating earthquakes in the future.

Last April, two earthquakes struck off the coast of Sumatra and sent people scrambling for higher ground anticipating a devastating tsunami that never came. Instead the earthquakes, which registered at 8.6 and 8.2 in magnitude, were the largest ocean strike-slip quakes ever recorded and ruptured at depths five times greater than expected. These new developments are challenging seismologists’ notions of strike-slip earthquakes and raising new questions about the region’s tectonics. “Oceanic strike-slip earthquakes are helping us learn what’s happening at the plate boundary where the 2004 earthquake happened, how exactly it happened, and if another one is likely to occur,” said Abercrombie. “This kind of research has implications for seismic hazard maps in this part of the world,” she said.

When she isn’t in the lab, Kasey spends time playing soccer with friends or volunteering at the MSPCA. But what she enjoys most is teaching. She spent her first semester at Boston University teaching a class on natural disasters. For Kasey, teaching people about how their planet works fulfills her and is a career she wants to pursue. “I want to explain to future students why their world is organized this way and what we still don’t understand,” she said. “The earth is actually here where we can see and feel it, and people love learning about their own environment.”

Recently, Kasey dropped by a Boston middle school class to talk to students about earthquakes. Her colleague, friend, and roommate Alistair Hayden teaches the class as part of the Glacier Program, which places graduate students in middle schools to teach earth science. During the visit, she showed the students a seismic hazard map of Boston. “Their school was in a zone that wasn’t so great, but it wasn’t as bad as BU,” she said. Boston University was built on reclaimed land. If a magnitude 6 earthquake ruptured, which according to Kasey is not impossible, the earth beneath the surface would liquefy and the buildings of the university would sink. “They asked why we don’t have earthquake drills. We probably should, because it’s possible to have an intense earthquake here, they just occur over a longer timescale,” she said. “I told the kids, ‘don’t run outside, you get under a table and hold on.’”

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