A method comprising: emitting, by a first seismic source positioned on a surface of Earth, a first seismic signal, wherein the first seismic source, a first seismic sensor, a second seismic sensor, and a second seismic source are each collinearly positioned in separate locations along a straight line, and wherein a direction of propagation of the first seismic signal extends from the first seismic sensor towards the second seismic sensor; detecting, by the first seismic sensor positioned on the surface of the Earth, the first seismic signal; detecting, by the second seismic sensor positioned on the surface of the Earth, the first seismic signal; emitting, by the second seismic source positioned on the surface of the Earth, a second seismic signal, wherein the second seismic source is arranged collinearly with the first seismic sensor and the second seismic sensor, wherein a direction of propagation of the second seismic signal extends from the second seismic sensor towards the first seismic sensor, and wherein the direction of propagation of the first seismic signal opposes the direction of propagation of the second seismic signal; detecting, by the first seismic sensor, the second seismic signal; detecting, by the second seismic sensor, the second seismic signal; identifying, relative to a first clock in the first seismic sensor, a first time (T A1) associated with a time of arrival of the first seismic signal at the first seismic sensor, and a second time (T A2) associated with a time of arrival of the second seismic signal at the first seismic sensor; identifying, relative to a second clock in the second seismic sensor, a third time (T B1) associated with a time of arrival of the first seismic signal at the second seismic sensor, and a fourth time (T B1) associated with a time of arrival of the second seismic signal at the second seismic sensor; and determining an offset of the first clock relative to the second clock using the first time, the second time, the third time, and the fourth time. emitting, by a first seismic source positioned on a surface of Earth, a first seismic signal, wherein the first seismic source, a first seismic sensor, a second seismic sensor, and a second seismic source are each collinearly positioned in separate locations along a straight line, and wherein a direction of propagation of the first seismic signal extends from the first seismic sensor towards the second seismic sensor; detecting, by the first seismic sensor positioned on the surface of the Earth, the first seismic signal; detecting, by the second seismic sensor positioned on the surface of the Earth, the first seismic signal; emitting, by the second seismic source positioned on the surface of the Earth, a second seismic signal, wherein the second seismic source is arranged collinearly with the first seismic sensor and the second seismic sensor, wherein a direction of propagation of the second seismic signal extends from the second seismic sensor towards the first seismic sensor, and wherein the direction of propagation of the first seismic signal opposes the direction of propagation of the second seismic signal; detecting, by the first seismic sensor, the second seismic signal; detecting, by the second seismic sensor, the second seismic signal; identifying, relative to a first clock in the first seismic sensor, a first time (T A1) associated with a time of arrival of the first seismic signal at the first seismic sensor, and a second time (T A2) associated with a time of arrival of the second seismic signal at the first seismic sensor; identifying, relative to a second clock in the second seismic sensor, a third time (T B1) associated with a time of arrival of the first seismic signal at the second seismic sensor, and a fourth time (T B1) associated with a time of arrival of the second seismic signal at the second seismic sensor; and determining an offset of the first clock relative to the second clock using the first time, the second time, the third time, and the fourth time.