DisastersApril 2012 Indian Ocean earthquake indicate s that a new tectonic plate is being born
The 11 April 2012 8.7 magnitude earthquake in the Indian Ocean, unlike its 2004 predecessor, did very little damage; it began at one fault, and when it reached an intersecting fault, it ruptured; in total, four different faults were ruptured over the course of 150 seconds; when earthquakes spread to connecting faults, the rupture rips along faults that branch away from the initial fault like branches of a river; the April 2012 earthquakes took a very different course, running along grid-like patterns and making 90 degree turns; the weird rupture pattern reflects the fact that the region is giving birth to a new tectonic plate
In 2004 a powerful earthquake ripped through the Indian Ocean on the coast of Sumatra. The tsunami killed more than 227,000 in fourteen different countries.
Eight years later, on 11 April 2012, one of the most powerful earthquakes ever recorded struck the same island, but the ensuing tsunami was just twelve inches high. The earthquake did very little damage, even if only five other earthquakes with higher magnitudes have ever been recorded.
The Christian Science Monitor reports that data from a global network of seismometers on the day of the earthquake revealed the quake was a strike-slip earthquake, the kind that races along the San Andreas Fault. Most strike-slip earthquakes occur when two sides of a fault jolt horizontally, displacing the ground sideways. Typically, these types of earthquakes do not shove the ocean floor upward, a required move for tsunami waves to generate.
Most tsunamis occur in earthquakes known as subduction earthquakes, which are the most powerful on the planet because they occur at plate boundaries where one tectonic plates grind against one another.
According to seismologists the, 11 April earthquake was one of the most powerful strike-slip earthquakes ever recorded.
“Not only was the quake of unparalleled power, it hit in the middle of a tectonic plate, not at a plate boundary, like the San Andreas Fault,” Thorne Lay, a professor of earth and planetary sciences at the University of California, Santa Cruz told theMonitor. “So already it has two unusual attributes.”
Intrigued by the earthquake, Lay and his team duplicated a blow-by-blow account of how the earthquake progressed and found that the earthquake was able to turn corners.
The earthquake began at one fault and when it reached an intersecting fault, it ruptured. In total, four different faults were ruptured over the course of 150 seconds. According to Lay, when earthquakes spread to connecting faults, the rupture rips along faults that branch away from the initial fault like branches of a river.
The earthquakes took a very different course running along grid-like patterns and making 90 degree turns.
“Here, they really do seem to go along perpendicular faults, and we haven’t seen anything like that with a big earthquake.” Lay told theMonitor.
Lay also said that the weird rupture pattern reflects the geological circumstances at play where the earthquake hit. This brought Lay and his team to the realization that the region is giving birth to a new tectonic plate.
The faults that were ruptured are basically the bones of an ancient volcanic seam that lies across the ocean floor, which is giving rise to new crust. The system fell silent forty-five million years ago, but the fractures it created in the tectonic plate are still there.
Matthias Delescluse, a marine geophysicist at Paris’ Ecole Normale Supérieure, has an analogy to describe the situation. “I like to represent it with the sidecar analogy, think of the Australia region of the plate as a motorbike, and the India region as a sidecar. Both are hurtling northward at a fast clip — for a tectonic plate at least — at about 2 inches (5 cm) per year. Now imagine the sidecar — not the motorbike — runs into a wall,” Delescluse told theMonitor.“The sidecar would compress, and the motor bike, depending on the violence of the shock, would finally detach from the sidecar.”
Evidence says that the Indo-Australian plate began to be ripped apart between eight million and ten million years ago.
A paper written last month suggests that the earthquake likely triggered other quakes around the world for a short time. The paper offers a new look at the geological setup for the earthquake.
“The fact that within six months we have understood this much — that is really quite impressive.” Hiroo Kanamori, a professor emeritus at Caltech, and a revered figure among geophysicists.
Kanamori said that advancements in instruments and technology have allowed scientists to make these observations and conclusions. “If this had happened 40 years ago, it would have taken a few years to even understand what it was.” Kanamori told OurAmazingPlanet.
— Read more in Fred F. Pollitz et al., “The 11 April 2012 east Indian Ocean earthquake triggered large aftershocks worldwide,” Nature (26 September 2012) (doi:10.1038/nature11504)
