Faster velocities indicated that the waves traveled through solid bedrock or where pores in weathered rock are filled with water. The researchers lowered the logging tool into the borehole and took measurements as it rose back to the surface. The logging tool sends out a seismic wave and records the wave's velocity, or how quickly it moves, as it travels away from the tool, explained Gu. Using a seismic logging tool, the researchers mapped the subsurface. The researchers logged-lowered instruments that can send and receive signals, or even take high-resolution images, down a borehole-a 115-foot deep borehole drilled into the valley floor at the NSF-funded Susquehanna Shale Hills Critical Zone Observatory, a forested research site in Penn State's Stone Valley Forest that sits atop the Rose Hill shale formation. Here we tried to expand our knowledge by doing geophysics, which is relatively more efficient." "We also had the materials from the boreholes, so we knew the mineral abundance and element composition. "In this study, we had the advantage of having previously drilled boreholes, so we knew at which depths geochemical changes happen," Gu said. The process is expensive and laborious, and it only reveals the geochemical information for that specific point in a watershed rather than the entire watershed, said Xin Gu, a postdoctoral scholar in EESI.
Traditional geochemical tests involve drilling a borehole 3 to 4 inches in diameter deep into the ground, collecting the soil and rock samples, and grinding and analyzing the chemical makeup of the samples in a laboratory.
In this study we used human-generated seismic waves-similar to the waves from earthquakes-to look under the surface." "At this point, however, we don't know where the water is or how it moves in the subsurface because we don't know what is down there. population gets their drinking water from groundwater, so we need to protect this valuable resource," said Susan Brantley, distinguished professor of geosciences and director of the Earth and Environmental Systems Institute (EESI) at Penn State. They usually travel slightly faster than the Rayleigh waves."About one third of the U.S. Love waves involve the motion of the ground side-to-side, perpendicular to the propagation velocity. They travel at roughly 90% of the speed of the S waves. Rayleigh waves or ground roll waves cause the surface of the ground to move up and down. Love who modeled them - definitely not an indication that anyone is fond of them). Waves whose amplitude of moton is parallel to the surface are called Love waves (named after the mathematician A. The waves which move the surface up and down are called Rayleigh waves and are sometimes described as "ground roll". They are typically more damaging than the P waves because they are several times higher in amplitude.Įarthquakes also produce surface waves which may cause motion perpendicular to the surface or parallel to the surface. S waves travel typically 60% of the speed of P waves. They travel only through solids, and the absence of detected S waves at large distances from earthquakes was the first indication that the Earth has a liquid core. S waves are transverse waves which involve movement of the ground perpendicular to the velocity of propagation. The P waves from an earthquake arrive first, but because of their small amplitudes don't do as much damage as the S waves and surface waves which follow. P waves depend upon the bulk modulus of elasticity for the material as well as its density, and the wave speed in a solid material like granite can be about 5000 m/s. Water can support P waves but not S waves, and the speed of these P waves (speed of sound) in water is about 1450 m/s. P waves in air are simply sound waves and the speed of sound is around 340 m/s for ordinary temperatures.
However, S waves depend upon a resistance to transverse or "shear" force which does not exist in a liquid or gas medium, so they can only travel in the solid parts of the Earth (see geologic example). Since any material, solid or liquid (fluid) is subject to compression, the P waves can travel through any kind of material. For seismic waves through the bulk material the longitudinal or compressional waves are called P waves (for "primary" waves) whereas the transverse waves are callled S waves ("secondary" waves). In a solid material these waves can be either longitudinal waves or transverse waves. The Earth's crust as a solid object will support waves through the crust called body waves and on the surface (surface waves). A disturbance like an earthquake at any point on the Earth will produce energetic waves called seismic waves. Since the Earth or any other planetary body can be considered to be an elastic object, it will support the propagation of traveling waves.