Context

A geologist assigned to make a preliminary study on the frequent tremors in Mizoram has said that Mizoram’s zone of “scary” earthquakes is caught between two subterranean faults.

About

• Mizoram experienced at least eight moderate earthquakes between June 21 and July 9. The tremors ranged from 4.2 to 5.5 on the Richter scale.
• The epicenter of most of these quakes was beneath the Champhai district bordering Myanmar, including the last one of magnitude 4.3 and about 10 kilometres deep. A few were beneath the adjoining Saitual and Serchhip districts.
• The tremors after the strongest of these earthquakes on June 22 have been aftershocks that can happen for a long time. But as long they are below the intensity of 5, there’s nothing to worry about.
• An aftershock of 5 or more on the Richter could be a sign of a major earthquake waiting to happen.

Recent Findings

• As per the study, earthquakes have happened and will happen in that part of Mizoram because it is caught between two geological faults. These are the Churachandpur Mao Fault and the Mat Fault.
• The Churachandpur Mao Fault is named after two places in Manipur and runs north-south into Myanmar along the border of Champhai.
• The Mat Fault runs northwest-southeast across Mizoram, beneath the river Mat near Serchhip.
• There are several shallower transverse or minor faults in between these two major faults that are deeper.

Faults

• A fault is a fracture in the crustal rocks wherein the rocks are displaced along a plane called ‘fault plane’. In other words, when the crustal rocks are displaced due to tensional forces caused by the endogenetic movements along a plane, the resultant structure is called a fault.
• In fact, ‘faulting involves differential movement of strata on either side of fault-plane (involving a single plane of shearing) or fault-zone (involving several closely spaced fault-planes) as a result of either compressional or tensional forces in the earth's crust.
• The differential movement may be upwards, downwards, horizontal, oblique, or even rotatory’.
• The study of fault geomorphology involves 3 aspects of faulting:
  • Types of displacement of rock blocks and thus resultant fault types
  • Tectonic expressions of faulting
  • Geomorphic expressions of faulting.
  • Based on different types of movements, as referred to above, different types of faults are created in the crustal rocks viz. normal and reverse faults, lateral or strike-slip faults (also known as transverse, tear or transcurrent faults) divided into two subtypes-right lateral or dextral fault and left lateral or sinistral fault, step faults.