There are currently multiple commercial seismography applications available, including mineral or hydrocarbon prospecting, groundwater investigations, environmental and hazardous waste site studies, archaeology and civil engineering.
Seismography is based on transmitting pressure waves from a source through the earth or sea, receiving these waves using a network of distributed sensors, and deducing the subsurface composition and features from the received signals. The cost and complexity of seismological surveys vary widely, but the two main drivers are:
- The cost, reliability and weight of cables connecting the sensors
- The cost of large numbers of seismographic sensors
GNSS systems broadcast very precise timing signals that can be used to derive an extremely accurate absolute time reference. This information can be received by seismography sources and sensors equipped with GNSS receivers. Time-tagging both transmitted and received seismic signals with this absolute time reference, and combining it with the measured GNSS positions of the sources and sensors, will remove the need for connecting cables. A single sensor connected to a PC carried in a backpack could be used to perform seismographic surveys.
This will considerably reduce the minimum cost of seismography surveys, and open up the lower end of the seismography market. It could be used for example by development agencies to locate sites for water wells; to survey potential archaeological sites before starting digs; or by local councils to perform hazardous waste site studies.
The main advantages of the system are:
- Cost, weight, reliability and portability: Only one portable sensor and a seismic source, each with a GNSS receiver, are required. No cables are needed.
- Compatibility with existing systems: The system is compatible with existing sensor technologies and processing software.
- Flexibility and accuracy: Sensors can be placed wherever desired, instead of being restricted to rectangular cable- based array grids.
- Real-time investigation: The operator can increase survey resolution in real-time by adding extra measurement points.
- Reduced environmental impact and constraints: Surveys can be performed in areas covered by vegetation or buildings.
The system also has potential applications in scientific seismology and natural disaster management. The accuracy of the GNSS timing signals will allow detailed variations in subsurface stress or composition to be measured over time. Installing a GNSS seismography network in earthquake/tsunami prone or volcanic areas could help predict earthquake or volcanic activity and reduce the impact of these events on the local population.
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