David Gubbins: Earth

David Gubbins is British university teacher. Explore interesting quotes on earth.
David Gubbins: 12   quotes 0   likes

“After a large earthquake the earth "rings" like a bell; this motion can be observed on sensitive instruments up to a month after a large event. These oscillations have specific frequencies which are properties of the whole earth and which can be measured very accurately indeed. The lowest frequency oscillation has a period of about one hour. Any combination of seismic waves can be represented as an equivalent combination of normal modes. In practice the mode representation is most useful at low frequency — for seismic waves above about 40 s — since at higher frequencies the number of modes becomes prohibitively large.”

David Gubbins

[Seismology and plate tectonics, 1990, http://books.google.com/books?id=tZRxPzwoChIC&pg=PA5] (p. 5)
Seismology and Plate Tectonics (1990)

“Earthquakes generate elastic waves when one block of material slides against another; the break between the two blocks being called a fault. Explosions generate elastic waves by an impulsive change in volume in the material. Small explosive charges are used in controlled-source seismic experiments in which the waves penetrate only a few kilometres into the earth.”

David Gubbins

(p. 12)
Seismology and Plate Tectonics (1990)

Change

“… since the Second World War… the proton magnetometer has revolutionized measurements, satellites have given new impetus to magnetic surveying, discoveries of large mineral deposits have maintained activity in conventional magnetic prospecting, and geomagnetism has continued to play a central role in major scientific developments such as plate tectonics (where the time scale of reversals of the polarity of the Earth's magnetic field still provides the main source of information on the movement of the plates.)”

David Gubbins
War , World , Time