Sumatra—A Tale Of Two Earthquakes & A Tale of Two Upcoming Tectonic Plates

Summary

In this video, we explore the contrast between two significant earthquakes: the 2004 magnitude 9.1 earthquake that triggered a devastating tsunami, and the 2012 magnitude 8.7 earthquake that caused minimal damage. Despite their similar magnitudes, these earthquakes resulted from different tectonic processes within the Indo-Australian Plate. The 2012 earthquake was an intra-plate strike-slip event, a rare occurrence for such a large magnitude, and highlighted the ongoing tectonic deformation of the plate, which could eventually lead to the creation of a new subduction zone. The complexity of the 2012 event sheds light on the intricate dynamics of plate tectonics.

Takeaways

• 😀 A magnitude 9.1 earthquake in 2004 triggered a devastating tsunami that killed over 230,000 people.
• 😀 A similar magnitude 8.7 earthquake in 2012 caused little damage and minimal ocean waves, despite being close in proximity.
• 😀 The two earthquakes were caused by different tectonic processes, despite their similar magnitude.
• 😀 The 2012 earthquake was the largest intra-plate earthquake and the largest strike-slip earthquake recorded.
• 😀 The Indo-Australian Plate is slowly pushing into Eurasia, causing strain in the region and affecting earthquake behavior.
• 😀 The 2004 earthquake occurred at the contact between two plates, generating a tsunami from the upward thrust of the plates.
• 😀 The 2012 earthquake happened 430 km west of the subduction zone, and was caused by a strike-slip fault, not a subduction zone.
• 😀 Geodetic data shows that Australia is moving northward at 5.6 cm per year, while India’s movement has slowed to 3.7 cm per year.
• 😀 This differential movement across the Indo-Australian Plate causes compression near its center, which may eventually lead to splitting into two sub-plates.
• 😀 The 2012 earthquake was a complex event, with multiple ruptures along different strike-slip faults, resulting in the equivalent of four magnitude 8 earthquakes.
• 😀 The Indo-Australian Plate is being compressed in the north and stretched in the south, possibly leading to the formation of a new subduction zone and island arcs similar to Sumatra and Japan.

Q & A

What caused the significant difference in the impact of the 2004 and 2012 earthquakes, despite their similar magnitudes?

The 2004 earthquake, a magnitude 9.1 event, was a subduction-zone earthquake, generating a massive tsunami due to upward thrust at the plate contact. The 2012 earthquake, with a magnitude of 8.7, was a strike-slip earthquake, occurring far from the subduction zone, causing minimal ocean waves and damage.

What makes the 2012 earthquake surprising in terms of its tectonic nature?

The 2012 earthquake was unusual because it was the largest intra-plate earthquake and the largest strike-slip earthquake ever recorded, occurring in a region typically associated with subduction-zone earthquakes.

What tectonic forces are influencing the Indo-Australian Plate's movements?

The Indo-Australian Plate is influenced by compression to the north, where it collides with the Eurasian Plate, and stretching due to slab pull, where the oceanic part of the plate is diving beneath the Sunda Plate.

How does the movement of the Indo-Australian Plate differ across its region?

Australia is moving northward at a rate of 5.6 cm per year, while India is pushing against the Himalayas, causing its movement to slow to 3.7 cm per year. This differential movement leads to compression and strain within the plate.

What potential geological outcome might result from the ongoing compression of the Indo-Australian Plate?

The compression may eventually lead to the division of the Indo-Australian Plate into two sub-plates: the Indian Plate and the Australian Plate, with significant tectonic consequences over millions of years.

What is unique about the earthquake's rupture pattern in the 2012 event?

The 2012 earthquake featured a complex rupture pattern, with an initial mainshock that propagated at over a kilometer per second along a right-lateral strike-slip fault. This triggered multiple subsequent ruptures, including left-lateral strike-slip ruptures, creating a highly complex earthquake.

How much total seismic energy did the 2012 earthquake release?

The total seismic energy released by the 2012 earthquake, resulting from multiple ruptures, was equivalent to four magnitude 8 earthquakes, which made it one of the most complex earthquakes ever recorded.

Why was the 2012 earthquake considered an intra-plate earthquake?

The 2012 earthquake was considered an intra-plate earthquake because it occurred within the Indo-Australian Plate itself, far from any subduction zone, making it distinct from typical plate boundary earthquakes.

How might the Indo-Australian Plate eventually form a new subduction zone?

Over millions of years, the southern part of the Indo-Australian Plate will likely be subducted beneath the Indian Plate, creating a new subduction zone, similar to those found near Sumatra and Japan.

What role does the curvature of the Earth play in the plate motions within the Indo-Australian Plate?

The curvature of the Earth complicates simple plate motion, as the strain and deformation are not uniform across the plate, especially when accounting for regional tectonic features such as the Himalayan collision zone.