Ma­jor earth­quake in Kash­mir is un­avoid­able In both re­gions of Jammu and Kash­mir the tec­tonic stress is ripe to host a ma­jor earth­quake

Views from Srinagar

Pakistan Observer - - KASHMIR - [Writer is As­sis­tant Professor in Struc­tural Ge­ol­ogy, Fac­ulty of Science, Univer­siti Brunei Darus­salam Jalan Tungku Link and cab be mailed at afroz.shah@gmail.com]

TDR AFROZ AH­MAD SHAH HE Mo­ment Mag­ni­tude (Mw) 7.8 earth­quake that oc­curred on 25th April 2015 in Nepal is ranked among the largest ever recorded in­stru­men­tal earth­quakes in Nepal since 1934, Bi­har-Nepal earth­quake of Mw 8.4, which killed about 15000 peo­ple.

This earth­quake was ex­pected, and was hosted on one of the seg­ments of Main Frontal Thrust (MFT), the megath­rust struc­ture that ac­com­mo­dates on an av­er­age some 2 cm/year of the re­gional con­ver­gence be­tween In­dia and Eura­sia plates. The to­tal length of this fault is more than 2000 kilo­me­ter, and it marks the present day ac­tive plate boundary along which ac­cu­mu­lated stress is oc­ca­sion­ally re­leased through medium to large mag­ni­tude earth­quakes.

Thus, it is not sur­pris­ing that the on­go­ing col­li­sion has re­sulted in more than seven ma­jor earth­quakes along the Hi­malayan arc in the past 100 years.

Jammu Kash­mir lies on the west of the ac­tive plate boundary, and it passed through Jammu city; how­ever, no trace of this fault has been mapped on sur­face in this re­gion, and thus it is as­sumed that it runs un­der as a blind struc­ture (have not rup­tured the sur­face) that con­trols the frontal-fold thrust belt in Jammu re­gion. The lat­est re­search demon­strates that there is a pos­si­bil­ity of a ma­jor earth­quake on this fault, which could hap­pen any­time be­cause cur­rently in Jammu re­gion and Kash­mir re­gion the tec­tonic stress is ripe to host such an earth­quake.

How­ever, the pres­ence of an­other ma­jor fault, the Ri­asi fault sys­tem, south of the Kash­mir basin, has also been seis­mi­cally quite for some time, and thus there is a pos­si­bil­ity that this fault could host a ma­jor earth­quake any­time soon. Im­por­tantly, this fault merges at depth with the frontal blind thrust, and thus there is pos­si­bil­ity that ma­jor earth­quake could ei­ther oc­cur on the Ri­asi fault sys­tem or the frontal fold-thrust belt, or both.

Such an earth­quake is es­ti­mated to be of (Mw > 8) or even big­ger, a much big­ger event than the Mw 7.6 earth­quake that oc­curred on the Balakot-Bagh fault in Pak­istan Azad Kash­mir in 2005. A well-doc­u­mented ma­jor fault sys­tem cuts through Kash­mir basin, and has the po­ten­tial to host Mw 7.6 or greater earth­quake. This fault sys­tem has not been stud­ies in de­tails, thus there are greater un­cer­tain­ties in un­der­stand­ing of this very fault.

Al­though, ge­o­mor­phic stud­ies clearly sug­gest that the fault is ac­tive, and has re­cently moved how­ever, only a de­tailed work in the fu­ture will shed more light on its ac­tiv­ity, and how much en­ergy has been re­leased through the fault.

With our cur­rent un­der­stand­ing of all the three ma­jor ac­tive earth­quake sources mapped in Jammu Kash­mir re­gion (from north these are: Kash­mir basin fault/Bala­por fault, Raisi fault, frontal fold-thrust belt) it is clear that a ma­jor or mega earth­quake is bound to hap­pen on ei­ther the Raisi fault or the frontal fold-thrust belt or both. This can oc­cur any­time: We un­der­stand the lim­i­ta­tions of a few stud­ies that have been done in Jammu, and Kash­mir re­gion to map, and un­der­stand the seis­mic risk, how­ever, the ma­jor dis­as­ter can­not be over­looked.

With many un­cer­tain­ties that re­main to un­der­stand the nu­cle­ation, prop­a­ga­tion, be­hav­ior, and stress ac­cu­mu­la­tion on faults, un­known ac­tive faults, it is safe to con­clude that ma­jor/mega earth­quake dis­as­ter is Kash­mir is un­avoid­able.

And for a reli­able seis­mic haz­ard and risk eval­u­a­tion some de­tailed pa­le­o­seis­mo­log­i­cal stud­ies are ex­tremely nec­es­sary to de­ter­mine the cur­rent sta­tus of strain ac­cu­mu­la­tion on faults/folds or fault-seg­ments. Fur­ther, our cur­rent knowl­edge about ma­jor earth­quakes sug­gest that they gen­er­ally do not fol­low a pat­tern, and oc­cur ran­domly any­time, thus the time since the last great his­tor­i­cal earth­quake is of no real sig­nif­i­cance.

This means that the con­cept of a rather reg­u­lar re­turn time be­tween cat­a­strophic earth­quakes is prob­a­bly not rel­e­vant for the Hi­malaya. Please un­der­stand that the earth­quake threat in Jammu Kash­mir is real and, it should not be taken lightly. Since the earth­quake science is at a stage where sci­en­tists more or less un­der­stand the cause of earth­quakes but are not very con­fi­dent about the pre­dic­tion of an in­com­ing event. This means that there is a need to un­der­stand how to live with earth­quakes with­out a suc­cess­ful pre­dic­tion in sight.

It can be achieved if we strictly abide by the strict con­struc­tion stan­dards, care­ful ge­o­log­i­cal eval­u­a­tion of build­ing sites, and pub­lic ed­u­ca­tion. This should be done now. —Courtresy: Ris­ing Kash­mir

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