Billion Dollar Question (Geographics)

Earthquake hits Indonesia, Why No Tsunami?




A massive earthquake of 8.9 magnitude struck off Indonesia's Sumatra island on April 11, 2012. The focus of the quake was 29 km from the surface

Why tremors were experienced in several parts of India?

Types of Fault

Tremors were felt at faraway locations (India) because

Earthquake produces surface waves. These surface waves cause a lateral movement of the particles in the earth's medium. The earth behaves like an elastic medium when these seismic waves travel. Why unlike December 26, 2004 Earthquake, no Tsunami this time? First, Some basics on types of Faults: 1.Strike Slip Fault: Fault rupture of the ground generates vibrations-or waves-in the rock that we feel as ground shaking. Faults are weaknesses in the rock and therefore earthquakes tend to occur over and over along the same faults For strike-slip faults, the rupture is nearly vertical and during an earthquake one side slides past the other The fractured crust slides past each other laterally. 2. Normal Fault: This type of fault occurs when ground on one side moves down the dip of the fault relative to the adjacent ground. 3. Thrust Fault: In thrust fault ground on one side of the fault moves up and over adjacent ground. Now, why no Tsunami this time???? The basis why the 8.6-magnitude earthquake did not cause killer tsunami waves was the nature of the faulting. The December 26, 2004 earthquake was caused by a ‘Thrust Fault’. The April 11, 2012 earthquake was caused by a ‘Strike-Slip Fault’. In order to generate monster tsunami waves, there should be huge vertical displacement of the water column, which happens only in the case of a Thrust fault (like in the case of the December 2004 earthquake) or a dip-slip fault. A Strike-slip fault will generally not generate tsunami waves. Although the earthquake was a strike-slip fault, there should have been a small amount of oblique movement along the fault.