Scientists at the University of Texas-Austin have made amazing strides in revealing the inner workings of “slow-slip earthquakes” which are the slower more gradual tremors detected around the earths hot-spots such as the Pacific’s “Ring of Fire”. Geologists have used seismic CT scans and complex supercomputers to examine a specific region off the coast of New Zealand. The new data is raising questions about connections between the “slow slip” quakes and their far more destructive and damaging earthquakes that produce deadly tsunamis in the area.
According to Phys.org,
“The insights will help scientists pinpoint why tectonic energy at subduction zones such as New Zealand’s Hikurangi subduction zone, a seismically active region where the Pacific tectonic plate dives—or subducts—beneath the country’s North Island, is sometimes released gently as slow slip, and other times as devastating, high-magnitude earthquakes.”
The work of the UT Austin team was published in Nature Geoscience for a special edition about subduction zones.
“Subduction zones are the biggest earthquake and tsunami factories on the planet,” said co-author Laura Wallace, a research scientist at UT Austin’s Institute for Geophysics (UTIG) and GNS Science in New Zealand. “With more research like this, we can really begin to understand the origin of different types of [earthquake] behavior at subduction zones.”
Understanding How The Earth’s Crust Stores Energy
According to Adrien Arnulf, a UTOIG scientist, this particular line of research is critical because understanding where and when a large subduction zone earthquake could occur will only happen once we solve the mystery of the slow-slip quakes. “If you ignore slow slip, you will miscalculate how much energy is stored and released as tectonic plates move around the planet,” he said.
Knowing how, when and where the slow slip events occur is important because these are similar to high magnitude quakes, in that they release the same amount of pent-up kinetic energy, merely at a slower rate. These quakes are so slow moving that up until about twenty years ago, they were undetectable by instruments.
Why Perform These Tests In New Zealand?
The Hikurangi zone off the coast of New Zealand is the best site to make this study of slow-slip quakes because they happen at much shallower depths there. Shallow enough to be imaged at a high resolution which can be done by recording the natural vibrations of the Earth there or by creating artificial seismic waves and projecting them into the sub-surface to generate an echo we can record.
Up until recently the computing power and algorithms to turn that seismic data into detailed imagery simply didn’t exist. But through using techniques for CT scanning similar to what is used in the medical field, geologists can identify seismic echoes in much greater detail then ever possible.
Not an Exact Simulation of Earthquakes, But Closer Than Ever
Together with UT Jackson School of Geosciences’ Grad student Jame Biemiller, Arnulf was able to develop a simulation for modeling how the faults around the Pacific move, showing where the faults had become weak and were building pressure. The biggest success wasn’t necessarily that the simulation was flawless, it was more of a guide to show us where our gaps in understanding the physics are.
“We don’t necessarily have the nail-in-the-coffin of how exactly shallow slow slip occurs,” said Biemiller, “but we tested one of the standard nails (rate-state friction) and found it doesn’t work as well as you’d expect. That means we can probably assume there are other processes involved in modulating slow slip, like cycles of fluid pressurization and release.”
Studies like this one coming out of the University of Texas could help us begin to understand and more accurately predict seismic events, now that we can finally take into account the slow-moving release of seismic pressure on the tectonic plates that for decades was too quiet and gradual to detect.