Question: Can you detect very low frequency waves?
About the article "Gravitational wave", section "Introduction".

Candidate passages:
Sensors relatively close to a nuclear event, or a high-explosive test simulating a nuclear event, can detect, using acoustic methods, the pressure produced by the blast.
These include infrasound microbarographs (acoustic pressure sensors) that detect very low-frequency sound waves in the atmosphere produced by natural and man-made events.
Closely related to the microbarographs, but detecting pressure waves in water, are hydro-acoustic sensors, both underwater microphones and specialized seismic sensors that detect the motion of islands. 
Other manifestations.
Low frequency (< 20 Hz) Rayleigh waves are inaudible, yet they can be detected by many mammals, birds, insects and spiders.
Human beings should be able to detect such Rayleigh waves through their Pacinian corpuscles, which are in the joints, although people do not seem to consciously respond to the signals.
Some animals seem to use Rayleigh waves to communicate.
In particular, some biologists theorize that elephants may use vocalizations to generate Rayleigh waves.
Since Rayleigh waves decay slowly, they should be detectable over long distances.
Note that these Rayleigh waves have a much higher frequency than Rayleigh waves generated by earthquakes.
After the 2004 Indian Ocean Earthquake, some people have speculated that Rayleigh waves served as a warning to animals to seek higher ground, allowing them to escape the more slowly traveling tsunami.
At this time, evidence for this is mostly anecdotal.
Other animal early warning systems may rely on an ability to sense infrasonic waves traveling through the air. 
LOFAR opens the window to the so far unexplored low-energy synchrotron radio waves, emitted by cosmic-ray electrons in weak magnetic fields.
Very little is known about the origin and evolution of cosmic magnetic fields.
The space around galaxies and between galaxies may all be magnetic, and LOFAR may be the first to detect weak radio emission from such regions.
LOFAR will also measure the Faraday effect, which is the rotation of polarization plane of low-frequency radio waves, and gives another tool to detect weak magnetic fields. 
A pulsar timing array is a set of millisecond pulsars that can be used to detect and analyse gravitational waves.
Such a detection would result from a detailed investigation of the arrival times of pulses emitted by these millisecond pulsars.
Millisecond pulsars are used because they appear not to be prone to the starquakes and accretion events which can affect the period of classical pulsars.
The most interesting influence on these propagation properties is low-frequency gravitational waves, with a frequency of 10−9 to 10−6 Hertz; the expected astrophysical sources of such gravitational waves are massive black hole binaries in the centres of merging galaxies, where tens of millions of solar masses are in orbit with a period between months and a few years.
The gravitational waves cause the time of arrival of the pulses to vary by a few tens of nanoseconds over their wavelength (so, for a frequency of 3 x 10 −8 Hz, one cycle per year, you would find that pulses arrive 20 ns early in July and 20 ns late in January).
This is an extremely delicate experiment, although millisecond pulsars are stable enough clocks that the time of arrival of the pulses can be predicted to the required accuracy; the experiments use collections of 20 to 50 pulsars to account for dispersion effects in the atmosphere and in the space between us and the pulsar.
It is necessary to monitor each pulsar roughly once a week; a higher cadence of observation would allow the detection of higher-frequency gravitational waves, but it is unclear whether there would be loud enough astrophysical sources at such frequencies.
It is not possible to get particularly accurate sky locations for the sources by this method - analysing timings for twenty pulsars would produce a region of uncertainty of 100 square degrees, a patch of sky about the size of the constellation Scutum which would contain at least thousands of merging galaxies. 
An assortment of time-synchronized sensors can characterize conventional or nuclear explosions.
One pilot study, the Active Radio Interferometer for Explosion Surveillance (ARIES).
This technique implements an operational system for monitoring ionospheric pressure waves resulting from surface or atmospheric nuclear or chemical explosives.
Explosions produce pressure waves that can be detected by measuring phase variations between signals generated by ground stations along two different paths to a satellite.
This is a very modernized version, on a larger scale, of World War I sound ranging.
As can many sensors, ARIES can be used for additional purposes.
Collaborations are being pursued with the Space Forecast Center to use ARIES data for total electron content measures on a global scale, and with the meteorology/global environment community to monitor global climate change (via tropospheric water vapor content measurements), and by the general ionospheric physics community to study travelling ionospheric disturbances.
Sensors relatively close to a nuclear event, or a high-explosive test simulating a nuclear event, can detect, using acoustic methods, the pressure produced by the blast.
These include infrasound microbarographs (acoustic pressure sensors) that detect very low-frequency sound waves in the atmosphere produced by natural and man-made events.
Closely related to the microbarographs, but detecting pressure waves in water, are hydro-acoustic sensors, both underwater microphones and specialized seismic sensors that detect the motion of islands.