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Jean François Semblat
π Planet

Earthquakes: a force of nature that can be tamed?

Jean-François Semblat, Head of mechanics and energy department at ENSTA Paris (IP Paris)

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.

Arti­fi­cial earthquakes

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. 

Con­trol­ling arti­fi­cial quakes

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. 

Ulti­mate dream: con­trol nat­ur­al quakes

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!

1https://​coquake​.eu
2https://​uma​.ens​ta​-paris​.fr
3Prof Avouac is a recent invit­ed researcher at Insti­tut Poly­tech­nique de Paris: https://​www​.poly​tech​nique​.edu/​f​r​/​c​o​n​t​e​n​t​/​d​e​s​-​s​e​i​s​m​e​s​-​a​u​-​r​a​l​e​n​t​i​-​s​o​u​s​-​l​e​s​-​c​a​s​cades

Contributors

Jean François Semblat
Jean-François Semblat
Head of mechanics and energy department at ENSTA Paris (IP Paris)

Jean-François Semblat’s research focuses on the propagation of seismic waves in geological layers during major earthquakes. Using numerical simulation methods, he studies their amplification, attenuation, liquefaction, and dynamic soil-structure interaction. He is a member of the scientific council of the French association for earthquake engineering, a professor at ENSTA-Paris, and the head of the Mechanics and Energy department at the Institut Polytechnique in Paris.