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