Long offset low frequency seismic surveys using optical fibers

A method for performing a long-offset refraction seismic survey of a subsurface area of interest using a fiber-optic cable positioned at or near to the earth's surface and extending between a first cable end closer to the area of interest and a second cable end further from the area of interest, the method comprising:

• connecting an interrogator to an end of the fiber-optic cable, wherein the interrogator is configured to emit light into the cable through the end and detect reflected light from the cable;
• simultaneously activating one or more low frequency seismic sources at multiple positions along a source line and operating the interrogator to collect seismic refraction data, wherein
• the source line extends between a first source activation position closer to the area of interest and a second source activation position further from the area of interest, and wherein activating the source comprises activating the source in at least the first and the second activation positions;
• wherein
• the second source activation position is offset at least 9 km from the first cable end, and
• the cable and source line extend in opposite directions away from the area of interest, and
• processing the collected refraction data to build up an image of or extract information about the subsurface area of interest.