Which Type of Data is Recorded During Seismic Surveys?
During seismic surveys, the type of data recorded is primarily known as seismic traces, which are also widely referred to as seismograms.
Understanding Seismic Traces and Seismograms
Seismic traces are fundamental measurements that capture the Earth's response to seismic energy. Specifically, they directly represent the "response of the elastic wavefield to velocity and density contrasts across interfaces of layers of rock or sediments as energy travels from a source through the subsurface." This means they record how seismic waves behave as they encounter different geological formations beneath the Earth's surface.
Key aspects of the data recorded during seismic surveys include:
- Elastic Wavefield Interaction: Seismic traces document how elastic waves, generated by a source (like a vibrator or an explosive charge), propagate through various rock and sediment layers.
- Velocity and Density Contrasts: As these waves travel, they encounter interfaces where the rock properties—specifically the velocity at which waves travel and the material's density—change. These changes cause portions of the wave energy to reflect or refract, and these reflections are precisely what the seismic traces capture.
- Subsurface Geological Insights: By analyzing the patterns and characteristics of these recorded traces, geophysicists can infer the depth, thickness, and properties of different rock layers. This allows for the creation of detailed images of the subsurface, crucial for identifying geological structures, potential resource reservoirs (e.g., oil, gas, water), and understanding tectonic processes.
What Seismograms Reveal
Each seismogram effectively acts as a snapshot of the ground's motion at a specific receiver location over time. The variations in the recorded energy (amplitude and travel time) in a seismogram provide vital information:
- Depth Information: The time it takes for a seismic wave to travel from the source, reflect off a subsurface layer, and return to the receiver indicates the depth of that layer.
- Material Properties: The strength and character of the reflections can reveal insights into the type of rock, its porosity, and even the fluids it might contain (e.g., water, oil, gas).
This recorded data undergoes extensive processing and interpretation to transform raw seismic traces into comprehensive geological models of the Earth's interior.
