Book contents
- Frontmatter
- Contents
- Preface
- 1 Seismology, the science of earthquakes
- 2 Fundamental equations of an elastic medium
- 3 Elastic waves
- 4 Normal mode theory
- 5 Reflection and refraction
- 6 Ray theory. Media of constant velocity
- 7 Ray theory. Media of variable velocity
- 8 Ray propagation in a spherical medium
- 9 Travel times and the structure of the Earth
- 10 Surface waves
- 11 Wave propagation in layered media
- 12 Wave dispersion. Phase and group velocities
- 13 Free oscillations of the Earth
- 14 Anelasticity and anisotropy
- 15 Focal parameters of earthquakes
- 16 The source mechanism
- 17 The seismic moment tensor
- 18 Models of fracture
- 19 Methods of determination of source mechanisms
- 20 Seismicity, seismotectonics, and seismic risk
- 21 Seismographs and seismograms
- Appendix 1 Vectors and tensors
- Appendix 2 Cyclindrical and spherical coordinates
- Appendix 3 Bessel and Legendre functions
- Appendix 4 Fourier transforms
- Appendix 5 Parameters of the Earth
- Appendix 6 The interior of the Earth
- Appendix 7 Important earthquakes
- Appendix 8 Problems and exercises
- Bibliography
- References
- Index
21 - Seismographs and seismograms
- Frontmatter
- Contents
- Preface
- 1 Seismology, the science of earthquakes
- 2 Fundamental equations of an elastic medium
- 3 Elastic waves
- 4 Normal mode theory
- 5 Reflection and refraction
- 6 Ray theory. Media of constant velocity
- 7 Ray theory. Media of variable velocity
- 8 Ray propagation in a spherical medium
- 9 Travel times and the structure of the Earth
- 10 Surface waves
- 11 Wave propagation in layered media
- 12 Wave dispersion. Phase and group velocities
- 13 Free oscillations of the Earth
- 14 Anelasticity and anisotropy
- 15 Focal parameters of earthquakes
- 16 The source mechanism
- 17 The seismic moment tensor
- 18 Models of fracture
- 19 Methods of determination of source mechanisms
- 20 Seismicity, seismotectonics, and seismic risk
- 21 Seismographs and seismograms
- Appendix 1 Vectors and tensors
- Appendix 2 Cyclindrical and spherical coordinates
- Appendix 3 Bessel and Legendre functions
- Appendix 4 Fourier transforms
- Appendix 5 Parameters of the Earth
- Appendix 6 The interior of the Earth
- Appendix 7 Important earthquakes
- Appendix 8 Problems and exercises
- Bibliography
- References
- Index
Summary
The historical evolution of seismographs
The oldest instrument used to detect the occurrence of an earthquake was probably constructed in China during the second century AD and is attributed to the philosopher Chian-hen. This instrument consisted in a bronze figure of a dragon with eight heads in whose mouths there were eight balls. Inside the figure there was some kind of pendular device that pushed the balls and made them fall when it was shaken by an earthquake. The figure was oriented in the geographic directions so that, upon the arrival of seismic waves, the corresponding ball will fall and show the occurrence and orientation of a shock. In Europe, the first instrument was a mercury seismoscope designed by De Haute-Feuille in 1703, consisting in a vessel with mercury connected by eight channels to eight cavities. Earthquakes will make the mercury flow into one or several of the cavities, indicating their orientations and sizes (quantities of mercury spilled). It is not certain that the instrument was actually built, although we have a description of it, but similar instruments were built in 1784 by Cavalli and in 1818 by Cacciatori (Ferrari, 1992). Vertical and horizontal pendulums started to be used around 1750. These instruments have an alarm to indicate the occurrence of an earthquake or a stylus attached to the mass that left a mark on sand or smoked plate of glass in which case they are called seismoscopes.
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- Chapter
- Information
- Principles of Seismology , pp. 402 - 422Publisher: Cambridge University PressPrint publication year: 2000