Un­der­stand­ing the Nepal quake and its ut­terly dev­as­tat­ing ef­fects

The China Post - - COMMENTARY - BY DEEPAK CHAM­LA­GAIN

Eighty-two years af­ter the great 1934 NepalBi­har earth­quake that reg­is­tered a mag­ni­tude of 8.2, Nepal was struck by a mag­ni­tude 7.8 (as mea­sured by the United States Ge­o­log­i­cal Sur­vey) quake on April 25.

The quake hit cen­tral Nepal at 11:56:26 lo­cal time, with its epi­cen­ter lo­cated roughly about 34 kilo­me­ters east-southeast of Lamjung.

The quake jolted cen­tral Nepal se­verely and to the south, it was felt in the north­ern states of In­dia — Bi­har and Ut­tar Pradesh.

Pre­lim­i­nary data on ca­su­al­ties has shown that at least 3,800 peo­ple have been killed and an­other 7,000 in­jured across the coun­try.

As the dam­age as­sess­ment has not been com­pleted and re­port on dam­ages from re­mote ar­eas of coun­try have yet to ar­rive, the num­ber of deaths and in­jured and prop­erty dam­aged will def­i­nitely be in­creas­ing.

The great Nepal quake and the re­sul­tant dam­ages have raised some se­ri­ous ques­tions se­ri­ously. Why are the Hi­malayas prone to earth­quakes? Why did the great earth­quake hit Nepal?

What are the rea­sons be­hind the mas­sive dam­age through­out the coun­try? Are the on­go­ing ef­forts enough, in terms of pre­pared­ness and pol­icy? And what should be the way for­ward to mit­i­gate the risk of an­other earth­quake?

How This Hap­pened

The Hi­malayas were formed due to con­tin­u­ous col­li­sion be­tween the In­dian and Ti­betan plates. With the for­ma­tion of the Hi­malayas, the re­gion has been dis­sected east-to-west by sev­eral faults, among which the Main Hi­malayan Thrust, a south­ern ex­pres­sion of the Main Frontal Thrust im­me­di­ately south of the Churia hills, is the ma­jor seis­mo­genic mega-thrust in the en­tire Hi­malayas.

Cur­rently, the con­ver­gence in the Hi­malayas is in the range of 20 mil­lime­ters per year. Be­cause of such a con­ver­gence, elas­tic strain is be­ing ac­cu­mu­lated rapidly, which has been re­flected in many seis­mo­tec­tonic re­searches and global po­si­tion sys­tem data for the Nepal Hi­malayas.

Over the last cen­tury, the Hi­malayan arc has been struck by four earth­quakes with mag­ni­tude of roughly 8.5 — namely 1897 (Shi­long earth­quake), 1905 (Kan­gra earth­quake), 1934 (NepalBi­har earth­quake), and 1950 (As­sam earth­quake) — caus­ing the deaths of thou­sands of peo­ple.

The 1905 Kan­gra earth­quake pro­duced se­vere dam­age in the Kan­gra area and, about 100 kilo­me­ters to the east, in the Dehradun area.

The es­ti­mated rup­ture is a roughly 280-kilo­me­ter-long seg­ment, from Kan­gra to Dehradun, that must have ex­tended east­ward to about 78 de­grees east, near the bor­der with Nepal.

The 1934 Nepal-Bi­har earth­quake was be­lieved to rup­ture a 200-to-300-kilo­me­ter-long seg­ment to the east of Kathmandu.

The area be­tween the 1905 Dehradun earth­quake and the 1934 Nepal-Bi­har earth­quake had not wit­nessed a mega-quake in the last 50 years.

This re­gion was widely con­sid­ered the Cen­tral Hi­malayan Seis­mic Gap and was ac­cu­mu­lat­ing elas­tic strain dur­ing the in­ter-seis­mic pe­riod be­cause the plate bound­ary mega-thrust, the Main Hi­malayan Thrust, is locked in be­tween the front of the Higher Hi­malayas and the Churia range.

The re­cent great quake was caused by the re­lease of ac­cu­mu­lated strain in this locked por­tion of the thrust. We geo­sci­en­tists had re­peat­edly in­di­cated the im­pend­ing great earth­quake in that re­gion through rig­or­ous re­search on the seis­mo­tec­ton­ics of the re­gion.

Thus, the cause be­hind the quake maybe due to the re­lease of long ac­cu­mu­lated strain en­ergy in the seis­mic gap.

More sci­en­tific ideas be­hind this quake can only be ad­vanced af­ter rig­or­ous anal­y­sis of the mea­sured data of this seis­mic se­quence.

Why So Much Dam­age

As new re­ports are in­com­ing, it is cer­tain that the ca­su­al­ties and dam­ages will ac­cel­er­ate. From pre­lim­i­nary re­ports of dam­ages in the Kathmandu Val­ley, it is clear that the soft sed­i­ment-filled basin se­verely am­pli­fied the quake.

In our own re­search on the ground re­sponse anal­y­sis of the Kathmandu Val­ley, it has been dis­cov­ered that the quake would be am­pli­fied five to eight times in ar­eas like Thamel, Ason, Sund­hara, Patan, Balaju, and the southeast of the val­ley.

The avail­able data on dam­age pat­terns showed mas­sive dam­ages in Bhak­ta­pur, Kathmandu and Patan due to the quake, which aligns with re­cent find­ings.

Be­sides, the val­ley pe­riph­ery has shown higher am­pli­fi­ca­tion when com­pared to the cen­tral part. Me­dia re­ports have con­firmed mas­sive dam­ages along the edge of the val­ley.

The ma­jor cause for the mas­sive dam­ages, there­fore, could be the am­pli­fi­ca­tion of the en­ergy of the seis­mic wave, be­cause the val­ley might have dis­played basin ge­om­e­try, to­pog­ra­phy, and val­ley ef­fects. Thus, we must con­sider the val­ley within a 2D domain, rather than the clas­si­cal 1D view.

Be­side th­ese, other parts of the coun­try might have suf­fered from to­pog­ra­phy ef­fects that ac­cel­er­ated the en­ergy of the seis­mic wave, re­sult­ing in ex­ten­sive dam­age.

The other causes for the dam­age are, of course, due to earth­quake — in­duced land­slide, ground rup­ture, etc.

How to Pre­pare

For the fu­ture, the gov­ern­ment needs to come up with strong, im­ple­mentable pro­grams that al­ways put lo­cals at the fore­front.

The key ar­eas that the gov­ern­ment should fo­cus on are re­vi­sion and manda­tory im­ple­men­ta­tion of na­tional build­ing codes, al­lo­ca­tion of fi­nan­cial re­sources un­der the dis­as­ter risk re­duc­tion bud­get code, re­search on earth­quake science, strong mon­i­tor­ing and eval­u­a­tion of the on­go­ing dis­as­ter risk re­duc­tion-re­lated ac­tiv­i­ties in terms of ef­fec­tive­ness and out­put.

Be­side th­ese, site-spe­cific seis­mic haz­ard as­sess­ment through seis­mic site ef­fect anal­y­sis and seis­mic mi­cro­zona­tion should be car­ried out in all ur­ban cen­ters at least.

The earth­quake is a very pe­cu­liar haz­ard in terms of on­set time and the ex­tent of dam­age. We need to ur­gently for­mu­late a sep­a­rate earth­quake risk re­duc­tion pol­icy and strat­egy to min­i­mize risks of earth­quake s in all sec­tors.

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