Citation: Hubbard, J. and Bradley, K., 2023. M6.5 earthquake in Afghanistan contrasts with recent quake in Tajikistan. Earthquake Insights, https://doi.org/10.62481/a2b52223
A M6.5 earthquake just occurred in Afghanistan, not far from where a M6.8 earthquake occurred in Tajikistan just last month - but with some critical differences.
The two earthquakes occurred in areas with subducting slabs oriented in opposite directions. The rainbow lines above represent the depth to the plate interface (red = shallow, blue = deep). The earthquake in Tajikistan last month was shallow: ~12 km depth. That places it well above its subducting slab, which is ~100 km deep here. (See lower cross section above.) It was also a strike-slip event - likely upper-plate deformation.
In contrast, today's earthquake in Afghanistan is deep: ~190 km depth. That places it well BELOW its subucting slab! (See upper cross section above.) This one was a thrust.
Some of this could be mislocation of the slab, but it is also true that there is a lot of deformation both above the slab and within the slab in a subduction zone.
In both cases, the earthquake was not expected to cause significant damage due to the low population density and relatively light shaking.
Another interesting aspect is that the location of today's earthquake produced persistent seismicity before this earthquake, all around the same depth. Actually, that pattern has existed for many years!
Surprise - the area of the quake in Afghanistan had a M7.5 in 2015. There was active deep seismicity there both before and after the M7.5. And, weirdly, the area of the quake in Tajikistan had a M7.2 in 2015! Interesting patterns to explore.