Why a Tsunami is unlikely after 8.6-magnitude earthquake in Indonesia

Courtesy: CNNIBN

The Indonesia earthquake that hit on Wednesday afternoon appears to have been a strike-slip earthquake. It is unlikely that there will be a devastating tsunami after Wednesday's 8.6-magnitude quake. 

Tsunamis are generated by displacement of water. In 2004 Indian Ocean earthquake, a megathrust displaced a lot of water vertically, like so. The 2004 earthquake was almost purely strike-slip. 

Strike-slip earthquakes are completely horizontal and there is no vertical displacement. Since the vertical displacement of this earthquake will be relatively limited, the amount of water displaced and therefore tsunami is also likely to be limited. 

The Indonesia earthquake that hit on Wednesday afternoon appears to have been a strike-slip earthquake. It is unlikely that there will be a devastating tsunami after Wednesday's 8.6-magnitude quake. 

Tsunamis are generated by displacement of water. In 2004 Indian Ocean earthquake, a megathrust displaced a lot of water vertically, like so. The 2004 earthquake was almost purely strike-slip. 

Strike-slip earthquakes are completely horizontal and there is no vertical displacement. Since the vertical displacement of this earthquake will be relatively limited, the amount of water displaced and therefore tsunami is also likely to be limited. 

Strike-slip earthquakes are completely horizontal and there is no vertical displacement.

A devastating tsunami is not likely, at least not like the 2004 one but it is uncertain exactly how large a tsunami this earthquake may generate. 

To generate a tsunami, you must have vertical uplift of water. It is not impossible for strike-slip earthquakes to generate vertical uplift of water, however. 

If the strike-slip movement is towards the continental slope, there may still be some vertical offset. 

If an earthquake occurs in an area with 100 m depth water and the strike-slip motion is towards shallower water and land. The huge 100 m stack of that water lying above the epicenter then moves towards land, too, where the water may only be 80 m deep. Suddenly you've just produced 20 m of vertical offset because you moved a 100 m deep stack of water to an area that's only 80 m deep. The strike-slip motion appears to be in ESE oblique against Indonesia, though, it is still doubtful that this will be a devastating tsunami.