Book contents
- Frontmatter
- Contents
- Preface
- 1 INTRODUCTION
- 2 CAUSE OF EARTHQUAKES
- 3 SEISMICITY AND PREDICTION OF EARTHQUAKES
- 4 INSTRUMENTS
- 5 SEISMIC PULSES AND THE INTERNAL STRUCTURE OF THE EARTH
- 6 QUANTIFICATION OF EARTHQUAKE SIZE
- 7 ATTENUATION
- 8 MICROSEISMS
- 9 TSUNAMIS
- Appendix Some important dates in the history of seismology
- References
- Index
8 - MICROSEISMS
Published online by Cambridge University Press: 12 September 2009
- Frontmatter
- Contents
- Preface
- 1 INTRODUCTION
- 2 CAUSE OF EARTHQUAKES
- 3 SEISMICITY AND PREDICTION OF EARTHQUAKES
- 4 INSTRUMENTS
- 5 SEISMIC PULSES AND THE INTERNAL STRUCTURE OF THE EARTH
- 6 QUANTIFICATION OF EARTHQUAKE SIZE
- 7 ATTENUATION
- 8 MICROSEISMS
- 9 TSUNAMIS
- Appendix Some important dates in the history of seismology
- References
- Index
Summary
The vibrations produced by earthquakes stood out on the earliest seismograms because of their larger amplitudes over a continuous background of weaker motions. Macelwane (1953) states that by 1887 John Milne had concluded that microseisms provided a background of unrest everywhere on earth. Some of this background noise could be explained by local disturbances such as traffic-generated vibrations, building (and other) vibrations due to human activities, and ground movements associated with wind and falling water. It was quickly realized that background noise was reduced when the seismograph was isolated from obvious sources of disturbance and placed on a foundation firmly attached to solid rock. However, there remained characteristic ground motions for which no local source was apparent. The most prominent of these were vibrations in the range of 2–10 s which rose and fell in amplitude with time and were stronger in winter than in summer (see, e.g., Iyer, 1964; Brune and Oliver, 1959).
Timoteo Bertelli in 1872 appears to have been the first to recognize that these disturbances correlated with barometric depressions (Gutenberg, 1958B). Bertelli proposed the term microseismi to describe the small movements, which he observed by watching the free end of a pendulum through a microscope. In 1900, Father Josi Algue correlated such microseisms with storms crossing the Philippine Islands (Carder and Eppley, 1959).
The mechanism by which storms produce microseisms was at first thought to be surf breaking along coasts (Wiechert, 1904).
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- Information
- An Introduction to Seismological ResearchHistory and Development, pp. 131 - 136Publisher: Cambridge University PressPrint publication year: 1990