Earthquakes: a force of nature that can be tamed?

Earth­quakes are nat­ur­al cata­strophes that hap­pen due to a sud­den rup­ture in the geo­lo­gic­al lay­ers of the Earth’s crust. Each year, there is at least one earth­quake, which pro­duces a mag­nitude over 8 [Richter scale, the energy level] some­where in the world, and a fur­ther 130 of a mag­nitude between 6 and 7. On aver­age, every minute there are two “mini” earth­quakes of a mag­nitude of 2 or more. 

Seis­mic events like these hap­pen due to move­ment of the tec­ton­ic plates; these out­er lay­ers of our plan­et gradu­ally move, some­times push­ing against one anoth­er. Even though this move­ment is rel­at­ively slow, the increas­ing force of the plates push­ing against one anoth­er res­ults in a huge amount of energy being stored where they meet. Energy that pro­gress­ively builds up over the course of months or years. 

Even­tu­ally the force becomes too great, and the two plates skid past one anoth­er releas­ing an immense burst of energy. That gen­er­ates seis­mic waves, the force of can be felt in the shak­ing we exper­i­ence dur­ing an earth­quake, res­ult­ing in heavy dam­age to build­ings, bridges and life­lines (e.g. water, gas). As such, sub­sequent dam­age can be colossal. The large 2011 Tohoku earth­quake in Japan, for example, cost the World bank ~$235bn.

Nat­ur­al earth­quakes aside, today there are a num­ber of man-made earth­quakes, too. Occur­ring due to vari­ous human activ­it­ies, these seis­mic events take the form of weak shak­ing gen­er­ated by trans­port sys­tems such as heavy trucks, or indus­tri­al facil­it­ies using tur­bines. Whilst these weak shakes tend not to be too trouble­some, there are oth­er stronger arti­fi­cial quakes. Strong shak­ing, for example, can be felt in neigh­bour­hoods that sur­round geo­therm­al plants (such as those in Stras­bourg or Basel), min­ing oper­a­tions or areas where hydraul­ic frac­tur­ing is per­formed. Such effects are called “anthrop­ic seis­mi­city” since they are due to human activities.

Tak­ing the example of hydraul­ic frac­tur­ing. It is a pro­cess which is used to obtain oil and gas trapped inside sol­id bed­rock, by pump­ing pres­sur­ised liquid under­ground. The res­ult is a series of cracks being cre­ated under­ground, releas­ing the hydro­car­bons from pock­ets that would oth­er­wise have remain trapped for mil­len­nia. As such, this tech­nique can induce sig­ni­fic­ant shak­ing or even activ­ate pre-exist­ing nat­ur­al fault lines between the geo­lo­gic­al lay­ers. Even though hydraul­ic frac­tur­ing is an import­ant meth­od of extract­ing oil, indus­tri­al activ­it­ies are often delayed or even for­bid­den because of the risks of quakes. 

Lub­ric­at­ing flu­ids could be injec­ted into the bed­rock so that the geo­lo­gic­al struc­tures ‘slide’ smoothly over each other.

Since the annoy­ances or dam­ages due to arti­fi­cial quakes can prove to be sig­ni­fic­ant, it is man­dat­ory to bal­ance the risk with the eco­nom­ic issues. Hence, sev­er­al aven­ues are under study to find an appro­pri­ate meth­od of pre­ven­tion. To reduce arti­fi­cial quakes, research has shown that it may be pos­sible to inject lub­ric­ant­ing flu­ids into the bed­rock so that the geo­lo­gic­al struc­tures gently “slide” against one anoth­er; releas­ing the energy in a gradu­al rather than bru­tal way. 

The CoQuake pro­ject, fun­ded by the European com­mis­sion, aims at con­trolling arti­fi­cial quakes in such a way¹. As such, ongo­ing research is being con­duc­ted in the frame­work of this pro­ject between Ecole Cent­rale de Nantes (Prof. Stefan­ou) and Insti­tut Poly­tech­nique de Par­is (POEMS, Dr Chail­lat, and IMSIA Labs at ENSTA Par­is). They com­bine lab exper­i­ments, com­plex mech­an­ic­al and seis­mo­lo­gic­al mod­els as well as advanced sim­u­la­tion methods. 

We have a PhD stu­dent (L. Bagur) who is study­ing the com­plex mech­an­ic­al pro­cesses that occur in man-made quakes using com­puter mod­els. Using a soft­ware known as COFFEE², the team can mod­el the effect­ive­ness of con­trolling quakes by inject­ing dif­fer­ent flu­ids, all the while tak­ing into account the extremely com­plex 3D lay­out of the geo­lo­gic­al lay­ers. The chal­lenge is to under­stand the dif­fer­ent slid­ing effects of flu­id pres­sures – sim­il­ar to what hap­pens with wind­screen wipers slip­ping or squeak­ing depend­ing on how much rain there is!

Of course, bey­ond the sci­entif­ic interest in the top­ic, there are huge eco­nom­ic and envir­on­ment­al bene­fits if we are able to reduce seis­mic prob­lems asso­ci­ated with hydraul­ic fracturing. 

For nat­ur­al quakes, we already know the cru­cial role of flu­ids in the trig­ger­ing of fault slips. It has been extens­ively stud­ied in the Cor­inth gulf – one of the most seis­mic areas in Europe. We could thus ima­gine being able to adjust the flu­id pres­sure at stra­tegic pos­i­tions to con­trol sta­bil­ity of fault lines.

This pos­sib­il­ity remains a very com­plex prob­lem on such a large scale. So, the idea is excit­ing but it will prob­ably need huge facil­it­ies to reach an effi­cient pro­cess. Such ideas are linked to on-going research con­duc­ted in the USA by Prof Avou­ac at Cal­tech³. He stud­ied the so-called slip defi­cit along act­ive fault lines in order to pre­dict the trig­ger­ing of large quakes. The idea is to quanti­fy the num­ber of earth­quakes that should have occurred over a giv­en peri­od of time in order to assess the prob­ab­il­ity of a large earth­quake occur­ring in the future in rela­tion to the build-up of forces in the tec­ton­ic plates.

In fact, the energy stor­age pro­cess around large faults may be slow. It may take dec­ades, so no news may often be bad news in the case of earth­quakes. But, one day, we may even­tu­ally be able to mas­ter and con­trol large earthquakes!