Dam­age due to shal­low tremors

Kentish Express Ashford & District - - WHY THE EARTH SHOOK -

SEIS­MOL­O­GISTS say the dam­age caused by Satur­day’s earth­quake is highly un­usual.

While some res­i­dents in Folkestone suf­fered se­vere struc­tural dam­age to their homes else­where in Dover, Deal, Ash­ford and Thanet, hardly any dam­age at all was caused, de­spite peo­ple feel­ing the tremors.

The earth­quake mea­sured 4.3 on the Richter Scale and vi­bra­tions were felt as far away as East Sus­sex and Es­sex. It was also felt in Calais and Boulogne.

Seis­mol­o­gist Roger Mus­son, from the Bri­tish Ge­o­log­i­cal Sur­vey (BGS), said: “Nor­mally what you get with Bri­tish earth­quakes is a less con­cen­trated pat­tern of dam­age but spread out over a wide area.

Dam­age

“Here, the dam­age is quite se­vere but re­stricted to one area, while other ar­eas have hardly seen any dam­age at all.”

Earth­quakes oc­cur at the bound­aries of ma­jor crustal plates and the UK sits on the Bri­tish Eura­sion plate.

The BGS be­lieve the shal­low depth at which Satur­day’s earth­quake be­gan ex­plains why the dam­age cen­tred on Folkestone. Al­though the epi­cen­tre was half­way be­tween New Rom­ney and the French coast, 12km out to sea, the depth the tremors were recorded at only 5km. Other Bri­tish earth­quakes have had depths of about 15km.

Mr Mus­son added: “The dam­age suf­fered de­pends on the lo­ca­tion and depth. What hap­pens is that the shock­waves from the epi­cen­tre will dis­tort, which can hap­pen in a num­ber of ways.

“Lo­cal ge­ol­ogy has a fo­cus­ing ef­fect on the seis­mic waves and the se­ries of vi­bra­tions can ar­rive at dif­fer­ent strengths and from dif­fer­ent di­rec­tions.

“It is a com­plex in­ter­ac­tion but it is pos­si­ble that the vi­bra­tions were dis­torted and ended up at Folkestone, with neigh­bour­ing ar­eas less af­fected.”

Ex­perts ex­pected earth­quakes of at least 4 on the Richter Scale ev­ery five to 10 years in Bri­tain. But they recorded about 20 earth­quakes of about 3.5 on the Richter Scale ev­ery month.

“They are much more com­mon than peo­ple think,” Mr Mus­son added.

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