MCT and MBT are active seismically. All Hydro-power plant structures should resist the highest expected earthquake in the region. Each Hydro-power is provided by electro-magnetic alarming system that stop the Hydro-power station before the earthquake wave reached. 

regards

In the collisional tectonic context of the indian and Eurasian mega-plates, in the Himalayas, talking about main thrusts in necessarily taking about active faults that will remain so in all probability for millions to tens of millions of years. Good adequate care must be taken in the design of all structures there, particularly major structures.

All thrust faults (MCT/MBT/MFT etc) within the Himalayan domain are seismically active, though not uniformly along and across Himalaya. All the thrusts are emergent faults from the Main Himalayan Thrust (MHT). Major earthquakes (>= 7.0) originate from MHT and rupture can propagate up dip; in some cases fresh rupture can continue to break the surface along either of these emergent thrusts ( e.g., 2005 Kashmir earthquake) or as new surface rupture (note that the 2015 Nepal earthquake didn't produce surface rupture).

Many HEP are located at or near these faults in the Himalaya. Site specific seismic design parameters (Through PSHA/ DSHA) are considered so that the built structure can withstand the expected acceleration due to seismic shaking during an earthquake.

Having said so one has to take care of the situation that structures are not sited on/close to active faults/ shear zones. In case of surface rupture where structure is located over/near it, no amount to seismic design can help. Check what happened to a dam at Taiwan during the 1999 Chi-Chi earthquake. Other than direct rupture during earthquake, structures can undergo distress during inter-seismic periods due to strain localisation along weak zones through tilting/warping/folding etc.

With this information hope the situation at Tala HEP can be better appreciated...

Dear Sujit Dasgupta Sir,NIRM have installed a Microseismic monitoring system at the powerhouse of Tala Hydropower Plant.There is a problem of Rockbolt failure in the powerhouse.I am trying to correlate it with the stress redistribution or with MCT/MBT. But the number of events everyday is generally one on an average and the magnitude is -1 to -3 (Negative value,on Richter scale).I am unable to correlate the rockbolt failure pattern.How should I approach to correlate the Microseismic activity to Rockbolt's failure.

 Possibly related to creep movement along some faults close to the Power House. Check for subtle ground deformation in and around the area.

Dear Sujit Dasgupta Sir,If there is any movement in rock at the powerhouse due to the local fault,these movements will generate microseismic signal but the microseismic monitoring is not supporting any local fault movement at the site.

Creep movements can generate microseismicity but not necessarily define  the creep. In Himalayan domain seismicity is so diffused that even small mag earthquakes (3-4+) do not define active planes.                                                            Let us look at the problem in a different way; if there is signature of continuous distress in PH (rock bolt failure etc) then such signatures must also distress nearby rock mass along some trend both within and outside the tunnel. My suggestion is to make attempt to first locate the area/zone/trend of such distress, if any and then go for seismic monitoring with a suitable design layout of stations. Take help of high resolution imagery to locate anomalous domains before geological field checks and deployment of seismic network.