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to a truly grand…scale 9。5。 as you will gatherfrom this； measuring earthquakes is not always an exact science； particularly wheninterpreting readings from remote locations。 at all events； both quakes were whopping。 the1960 quake not only caused widespread damage across coastal south america； but also set offa giant tsunami that rolled six thousand miles across the pacific and slapped away much ofdowntown hilo； hawaii； destroying five hundred buildings and killing sixty people。 similarwave surges claimed yet more victims as far away as japan and the philippines。
for pure； focused； devastation； however； probably the most intense earthquake in recordedhistory was one that struck鈥攁nd essentially shook to pieces鈥攍isbon； portugal； on all saintsday （november 1）； 1755。 just before ten in the morning； the city was hit by a suddensideways lurch now estimated at magnitude 9。0 and shaken ferociously for seven full minutes。
the convulsive force was so great that the water rushed out of the city鈥檚 harbor and returnedin a wave fifty feet high； adding to the destruction。 when at last the motion ceased； survivorsenjoyed just three minutes of calm before a second shock came； only slightly less severe thanthe first。 a third and final shock followed two hours later。 at the end of it all； sixty thousandpeople were dead and virtually every building for miles reduced to rubble。 the san franciscoearthquake of 1906； for parison； measured an estimated 7。8 on the richter scale andlasted less than thirty seconds。
earthquakes are fairly mon。 every day on average somewhere in the world there aretwo of magnitude 2。0 or greater鈥攖hat鈥檚 enough to give anyone nearby a pretty good jolt。
although they tend to cluster in certain places鈥攏otably around the rim of the pacific鈥攖heycan occur almost anywhere。 in the united states； only florida； eastern texas； and the uppermidwest seem鈥攕o far鈥攖o be almost entirely immune。 new england has had two quakes ofmagnitude 6。0 or greater in the last two hundred years。 in april 2002； the region experienceda 5。1 magnitude shaking in a quake near lake champlain on the new york鈥搗ermont border；causing extensive local damage and （i can attest） knocking pictures from walls and childrenfrom beds as far away as new hampshire。
the most mon types of earthquakes are those where two plates meet； as in californiaalong the san andreas fault。 as the plates push against each other； pressures build up untilone or the other gives way。 in general； the longer the interval between quakes； the greater thepent…up pressure and thus the greater the scope for a really big jolt。 this is a particular worryfor tokyo； which bill mcguire； a hazards specialist at university college london； describesas 鈥渢he city waiting to die鈥潯。╪ot a motto you will find on many tourism leaflets）。 tokyo standson the boundary of three tectonic plates in a country already well known for its seismicinstability。 in 1995； as you will remember； the city of kobe； three hundred miles to the west；was struck by a magnitude 7。2 quake； which killed 6；394 people。 the damage was estimatedat 99 billion。 but that was as nothing鈥攚ell； as paratively little鈥攑ared with whatmay await tokyo。
tokyo has already suffered one of the most devastating earthquakes in modern times。 onseptember 1； 1923； just before noon； the city was hit by what is known as the great kantoquake鈥攁n event more than ten times more powerful than kobe鈥檚 earthquake。 two hundredthousand people were killed。 since that time； tokyo has been eerily quiet； so the strainbeneath the surface has been building for eighty years。 eventually it is bound to snap。 in 1923；tokyo had a population of about three million。 today it is approaching thirty million。 nobodycares to guess how many people might die； but the potential economic cost has been put ashigh as 7 trillion。
even more unnerving； because they are less well understood and capable of occurringanywhere at any time； are the rarer type of shakings known as intraplate quakes。 thesehappen away from plate boundaries； which makes them wholly unpredictable。 and becausethey e from a much greater depth； they tend to propagate over much wider areas。 themost notorious such quakes ever to hit the united states were a series of three in newmadrid； missouri； in the winter of 1811鈥�12。 the adventure started just after midnight on december 16 when people were awakened first by the noise of panicking farm animals （therestiveness of animals before quakes is not an old wives鈥櫋ale； but is in fact well established；though not at all understood） and then by an almighty rupturing noise from deep within theearth。 emerging from their houses； locals found the land rolling in waves up to three feet highand opening up in fissures several feet deep。 a strong smell of sulfur filled the air。 theshaking lasted for four minutes with the usual devastating effects to property。 among thewitnesses was the artist john james audubon； who happened to be in the area。 the quakeradiated outward with such force that it knocked down chimneys in cincinnati four hundredmiles away and； according to at least one account； 鈥渨recked boats in east coast harbors and 。
。 。 even collapsed scaffolding erected around the capitol building in washington； d。c。鈥潯njanuary 23 and february 4 further quakes of similar magnitude followed。 new madrid hasbeen silent ever since鈥攂ut not surprisingly； since such episodes have never been known tohappen in the same place twice。 as far as we know； they are as random as lightning。 the nextone could be under chicago or paris or kinshasa。 no one can even begin to guess。 and whatcauses these massive intraplate rupturings？ something deep within the earth。 more than thatwe don鈥檛 know。
by the 1960s scientists had grown sufficiently frustrated by how little they understood ofthe earth鈥檚 interior that they decided to try to do something about it。 specifically； they got theidea to drill through the ocean floor （the continental crust was too thick） to the mohodiscontinuity and to extract a piece of the earth鈥檚 mantle for examination at leisure。 thethinking was that if they could understand the nature of the rocks inside the earth； they mightbegin