How satellites are redefining earthquake science

A few months after its launch in 2022, the Sur­face Water and Ocean Topo­gra­phy (SWOT) satel­lite sur­pri­sed scien­tists. While its ini­tial mis­sion was to pro­vide water level mea­su­re­ments to hydro­lo­gists and ocea­no­gra­phers, in 2023 it detec­ted a tsu­na­mi in the Paci­fic¹. In May 2025, ano­ther tsu­na­mi was cap­tu­red by SWOT fol­lo­wing an ear­th­quake in Drake Pas­sage, loca­ted bet­ween the Paci­fic and Atlan­tic oceans. “In this remote part of the globe […], in situ seis­mo­lo­gi­cal and tsu­na­mi mea­su­re­ments remain extre­me­ly rare. […] SWOT could help to bet­ter unders­tand the tec­to­nic fea­tures of a poor­ly known area […],” writes the French Natio­nal Centre for Space Stu­dies (CNES)².

Until now, seis­mo­me­ters have been the main ins­tru­ment used by seis­mo­lo­gists, but satel­lites have recent­ly become valuable allies in the stu­dy of ear­th­quakes. In 2001, thanks to satel­lites, par­ti­cu­lar­ly conti­nuous GPS mea­su­re­ments, a com­ple­te­ly new type of ear­th­quake was dis­co­ve­red in sub­duc­tion zones : slow ear­th­quakes. These are ear­th­quakes that last for seve­ral days or even months and are com­ple­te­ly imper­cep­tible to seis­mo­me­ters and popu­la­tions³.

“The quan­ti­ty and qua­li­ty of satel­lite-geo­de­tic mea­su­re­ments of tec­to­nic defor­ma­tion have increa­sed dra­ma­ti­cal­ly over the past two decades impro­ving our abi­li­ty to observe active tec­to­nic pro­cesses,” wrote a Bri­tish research team in an article publi­shed in Nature Com­mu­ni­ca­tions in 2016⁴. Two types of satel­lites are used to stu­dy ear­th­quakes : Earth obser­va­tion satel­lites and posi­tio­ning satel­lites, such as GPS.

“Laun­ched in 1972, the Land­sat mis­sion offers, for the first time, a view of large fault zones [Editor’s note : where ear­th­quakes ori­gi­nate] on a regio­nal scale,” says Cécile Las­serre, direc­tor of geo­de­sy research at the CNRS. “One of the first land­mark stu­dies⁵ was publi­shed in 1977. Thanks to these images, the major faults in the col­li­sion zone bet­ween India and Asia (from the Hima­layas to Lake Bai­kal) were map­ped for the first time.” As the reso­lu­tion of ins­tru­ments increases with space mis­sions, these opti­cal satel­lites, which cap­ture images of the Earth like a came­ra, offer geo­lo­gists the pos­si­bi­li­ty of making increa­sin­gly detai­led maps of the fault lines where ear­th­quakes occur.

Scien­tists are see­king to exploit this space data in dif­ferent ways. The life of a fault fol­lows a cycle mar­ked by quiet per­iods inter­sper­sed with ear­th­quakes, with ground dis­pla­ce­ment accu­mu­la­ting over time. Natu­ral fea­tures, such as val­leys or moun­tain slopes, can be shif­ted seve­ral kilo­metres on either side of the fault. Scien­tists mea­sure these shifts and deter­mine how long it takes for these fea­tures to move. It then becomes pos­sible to mea­sure the speed at which faults have moved over the last few mil­len­nia, enabling seis­mic risk to be assessed.

In the 2000s, satel­lite ins­tru­ments ente­red a new era : they became capable of recor­ding images with a spa­tial reso­lu­tion of less than one metre (sub-meter reso­lu­tion). “Achie­ving this level of reso­lu­tion means that, for the first time, we can mea­sure ground dis­pla­ce­ment during a single ear­th­quake from space, as this is the scale of dis­pla­ce­ment cau­sed by major ear­th­quakes,” explains Cécile Las­serre. By com­pa­ring satel­lite images taken before and after the ear­th­quake, it is pos­sible not only to map the rup­ture, but also to quan­ti­fy the dis­pla­ce­ment. In 2004, a French team⁶ pro­vi­ded the first map of the dis­pla­ce­ments that occur­red along a fault during a major ear­th­quake in Tibet in 2001. “It is very dif­fi­cult to do the same work in the field, as the rup­ture exten­ded over a length of 450 km!” says Cécile Las­serre. “This data revea­led pre­vious­ly unk­nown com­plexi­ties and enabled us to improve our unders­tan­ding of earthquakes.”

Pre­vious­ly, we would set up sta­tions for a few days each year, but now very dense net­works have been per­ma­nent­ly deployed in cer­tain countries.

To com­plete the range of satel­lite ins­tru­ments used to stu­dy ear­th­quakes, we must also men­tion radar satel­lites. In 1992, radar images made it pos­sible for the first time to mea­sure the defor­ma­tion cau­sed by an ear­th­quake, the Lan­ders ear­th­quake in Cali­for­nia⁷. Unlike opti­cal satel­lites such as Land­sat or Spot, radar satel­lites emit a radar wave that is reflec­ted off the Earth’s sur­face. By com­pa­ring these images before and after an ear­th­quake, it is pos­sible to mea­sure the defor­ma­tion of the ground. “The latest gene­ra­tions of radar satel­lites can mea­sure dis­pla­ce­ment speeds of around one mil­li­metre per year,” explains Cécile Las­serre. “With such pre­ci­sion, it is pos­sible to stu­dy the dif­ferent phases of the seis­mic cycle : during, imme­dia­te­ly after and bet­ween earthquakes.”

“At the same time, GNSS mea­su­re­ments have been deve­lo­ped : these are high­ly com­ple­men­ta­ry to opti­cal and radar ima­ging mea­su­re­ments,” points out Cécile Las­serre. As explai­ned above, it is thanks to conti­nuous GPS mea­su­re­ments that slow ear­th­quakes have been dis­co­ve­red. The prin­ciple is simple : the pre­cise geo­gra­phi­cal posi­tion of a ground-based ins­tru­ment is mea­su­red using dedi­ca­ted GNSS satel­lites (GPS and Gali­leo, for example). This makes it pos­sible to record ground move­ments very accu­ra­te­ly, year after year. “Before, we used to set up sta­tions for a few days each year,” recalls Cécile Las­serre. “Now, very dense net­works have been per­ma­nent­ly deployed in cer­tain coun­tries.” All this spa­tial data, com­bi­ned with field mea­su­re­ments, gives scien­tists a bet­ter unders­tan­ding of the Earth’s defor­ma­tion pro­cesses, which is essen­tial for redu­cing the risks asso­cia­ted with these natu­ral disas­ters⁸.

Beyond the pure­ly scien­ti­fic aspect, satel­lites are also inva­luable for relief efforts during devas­ta­ting ear­th­quakes. In 2000, seve­ral space agen­cies (Euro­pean, French and Cana­dian) crea­ted and joi­ned the Inter­na­tio­nal Char­ter on Space and Major Disas­ters,⁹. “The role of the Char­ter is to pro­vide satel­lite data free of charge during major disas­ters anyw­here in the world,” explains Claire Huber, risk engi­neer at SERTIT Uni­ver­si­ty of Stras­bourg. “As an ope­ra­tor, our role is to trans­form satel­lite infor­ma­tion into maps that can be read by eve­ryone and pro­vide a glo­bal view of the event.” When an orga­ni­sa­tion requests assis­tance from the Char­ter, ope­ra­tors pro­gramme the satel­lites into “urgent” mode to obtain images of the disas­ter-stri­cken area as qui­ck­ly as pos­sible. “We map visible damage to buil­dings, blo­cked roads and popu­la­tion gathe­rings,” explains Claire Huber. “This data is very impor­tant for deploying relief efforts as effec­ti­ve­ly and qui­ck­ly as pos­sible to the most affec­ted areas.” Although they can never com­ple­te­ly replace field mea­su­re­ments, satel­lites have become indis­pen­sable for moni­to­ring the planet.

Anaïs Maréchal