WHY IN NEWS ?
- Recently, earthquake of 6.3 magnitude, which occurred near the far western terminus of the Hindu Kush Mountain range in Afghanistan, was followed by another 6.3 magnitude quake 30 minutes later.
MORE ABOUT THE NEWS:
- According to the U.S. Geological Survey (USGS): The first earthquake was followed by a second earthquake [with 6.3 magnitude] that occurred approximately 30 minutes later.
- Both earthquakes occurred on east west striking fault planes that dip to either the north or south.
- The earthquakes occurred within the Eurasia plate in an intracontinental mountain belt.
- There were about a half a dozen aftershocks following the earthquakes.
CAUSES OF TWIN EARTHQUAKES:
- All earthquakes have been thrust faults, otherwise known as reverse faults.
- Thrust faults form due to horizontal compressive stresses and so cause shortening of the crust.
- Here one block or wall (the hanging wall) moves up relative to the other (called the footwall).
- Earthquakes are generally followed by aftershocks of relatively lesser magnitude.
- A quake of 6.3 magnitude was followed by another of the same magnitude.
- This can happen when a fault at one place ruptures resulting in an earthquake that releases the stress.
- The release of stress in one fault results in the loading of stress at another fault.
- The loading of stress can result in another earthquake which can be of similar magnitude or even higher magnitude.
- But the magnitude will not be smaller than the first quake
OTHER REGIONAL CAUSES OF TWIN EARTHQUAKES:
- In subduction zones and in the Himalayas where there is interaction between two continental plates, the fault lengths can be very large and also very wide.
- That is the reason why an earthquake in the fault can trigger another in the same fault.
- The second earthquake occurred quite close to the first one (about 20 km distance) in the same fault.
- Earthquakes are quite common in Afghanistan due to active interactions between three tectonic plates — the Arabia, Eurasia, and India plates.
- According to the USGS, earthquakes in western and central Afghanistan are “primarily influenced by the northward movement of the Arabia plate relative to the Eurasia plate.”
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