Digging down deep for earthquake studies
MILWAUKEE — To understand earthquakes, scientists are going straight to their source.
Geologists are drilling miles-deep into the earth, directly through the faults where the plates that make up the Earth’s crust come into contact.
It is a bold plan and part of two experiments taking place at dangerous faults in New Zealand and Japan. These are faults that could erupt at any moment, causing massive earthquakes.
“These are the natural disasters that kill the most people on the planet. So we need to know as well as we can how they work and whether there are ways to (lessen) their effects by early warning or detection,” said Harold Tobin, a professor in the department of geoscience at the University of Wisconsin-Madison.
Ready To Dig Deep
To understand the chain of events that trigger such massive quakes, the scientists from the university will take samples of rock from holes and record the conditions down deep. If they’re lucky, they will catch a quake in action.
Earthquakes are some of the most destructive and deadly natural disasters on the planet. They also are some of the least predictable. Scientists can say how likely a fault is to experience a quake, but they can only predict earthquakes over the span of decades. They are unable to give early warnings — not very helpful for people living in the area who have only moments to take cover.
Scientists don’t know how — or even if — it might be possible to predict earthquakes. Part of the problem is they know so little about how earthquakes start. The phenomenon begins deep below the surface of the Earth, too deep for researchers to go.
Waves Of Energy
Typically, earthquakes are studied by measuring seismic waves, which are waves of energy that come from tremors within the Earth when the plates bump up against each other. This information is useful, but it’s indirect. It’s sort of like trying to figure out what’s inside your birthday present by shaking the box around — you would know much more if you could unwrap it and look directly at what was inside.
This is why the scientists want to drill down to the fault line. They will bring up core samples of rock as they drill, to study their properties. Then they will place instruments in the hole to measure seismic tremors and other important characteristics of the fault zone. These include the pressure, temperature, and stresses and strains on the rocks, as well as properties of groundwater in the area.
“If we want to understand earthquakes, it’s one of the few kind of direct ways we can get evidence about what faults are like,” said Clifford Thurber. He is a professor in the department of geoscience at UW-Madison.
Thurber and Tobin are part of an international group of scientists working on the Deep Fault Drilling Project. The experiment studies the Alpine Fault in New Zealand.
Fault Due For Quake
This fault has been quiet since 1717. It typically produces a major quake every 300 or 400 years. Scientists therefore think the fault is due for an earthquake, estimating a 28 percent chance of a quake in the next 50 years. Beginning in October, experimenters will drill nearly a mile deep into the Alpine Fault.
Drilling such holes, however, is no easy task. This is especially true for faults that are under water, as many of the most dangerous, tsunami-generating faults are.
Tobin is co-chief scientist of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) in Japan. He spent seven weeks at sea last winter on a scientific drilling ship called the Chikyu, drilling into the Nankai Fault off the coast of southern Japan.
At times braving harsh winds and waves as high as 30 feet, Tobin and his fellow scientists took round-the-clock shifts, analyzing the data and samples of rock that came out of the borehole. The hole is currently more than halfway to its planned depth of three miles below the seabed.
Instruments will remain in the boreholes of both experiments for decades. They will quietly collect data, waiting for an earthquake that could strike at any time.
Pushing Past Setbacks
The UW researchers also were involved in an earlier experiment, the San Andreas Fault Observatory at Depth (SAFOD). The experiment was completed in 2007. Scientists drilled a 2-mile-deep hole that pierced the famous San Andreas Fault in California that has caused so many earthquakes throughout the state.
The experiment recovered some of the first samples of rock at the depth where small earthquakes can originate.
However, scientists encountered many setbacks. Drilling was more expensive than expected, due to rising oil prices. Also, instruments placed in the hole failed shortly after they were installed. This was due to harmful gases, crushing pressures and high temperatures at that depth.
“The whole thing is just like a cauldron down there,” Thurber said.
The lessons scientists learned there will be applied to the experiments in New Zealand and Japan.
These experiments won’t quite reach the depth where major quakes start. But they will gain valuable information about how faults behave close to the source. Scientists will also learn how earthquakes travel along the fault when they erupt.
“We’re seeing rocks much closer to what they are like down where earthquakes do their thing,” Thurber said.