1. Introduction to Seismology
Lupei Zhu

2. Introduction to Seismology
Topics
What is seismology?
Seismic sources and waves
Seismic stations and seismograms
Global earthquake distribution
Spatial distribution
Seismic hazard
A brief history of seismology
Development in instrument
Major discoveries about Earth interior by seismology
SLU’s contribution
What is the relationship between seismology and nuclear weapons?
Introduction to Seismology

3. Introduction to Seismology
What is Seismology ?
Seism- or seismo-, from Greek seismos, means earthquake, vibration.
Seismology is a science that deals with earthquakes and with naturally/artificially produced vibrations of the earth.
Introduction to Seismology

4. Introduction to Seismology
Seismic Sources
The most common sources of earth vibration are earthquakes, however there are lots of other sources including:
Explosions (chemical and nuclear)
Landslides
Volcanic eruptions
Weather (wind, surf, storms)
Cultural noise (traffic, supersonic aircraft, etc.)
Introduction to Seismology

5. Introduction to Seismology
Seismic Waves
The vibration, or disturbance, generated by the seismic source propagates outward in the form of seismic waves. See 'P' and 'S' waves explored
Introduction to Seismology

6. Introduction to Seismology
Seismometer
an instrument that senses ground motion and converts the motion into some form of signal.
Introduction to Seismology

7. Introduction to Seismology
Seismograph
a system of instruments that detects and records ground vibration. See example
A seismic station hosts one or more seismographs
Introduction to Seismology

8. Introduction to Seismology
Seismogram
An actual record of ground motion produced by a seismograph.
Introduction to Seismology

9. Introduction to Seismology
Seismicity
The relative frequency and distribution of earthquakes.
Introduction to Seismology

10. Introduction to Seismology
Seismic Hazard
Introduction to Seismology

11. A Brief History of Seismology
Earthquakes have been a major hazard to mankind. Many early civilizations kept description of large earthquakes, in forms of writing (e.g. Chinese) or story-telling (e.g. Indians).
The world’s first seismoscope was constructed by Chang Heng of China in 132 AD.
Introduction to Seismology

12. A Brief History of Seismology
1822: Poisson derived that there are two types of waves, P- and S- waves, in solids.
The first true seismograph was invented by Cecchi of Italy in
The first seismometer that use a electromagnetic transducer to sense ground motion was invented by Galitzin of Russia in
Introduction to Seismology

13. A Brief History of Seismology
1909: Mohorovicic discovered a major interface in the Earth that separates the crust from the mantle. It was named after him (Moho).
1914: Gutenberg discovered the liquid core of the Earth.
1936: Lehmann identified the solid inner core.
1956: Bullen established the first layered model of the Earth.
Introduction to Seismology

14. Introduction to Seismology
SLU’s Contributions
The first SLU seismometer was installed in 1909 (in basement of DuBourg Hall)
It was part of the first North American seismological network – the Jesuit Seismological Network
The first geophysics department in the Western hemisphere was established at SLU in 1925, by J.B. Macelwane, S.J.
At SLU in 1948 Florence Robinson became the first woman geophysicist to obtain a PhD in North America
Introduction to Seismology

15. Introduction to Seismology
SLU’s Contributions
Introduction to Seismology

16. Seismology and Nuclear Weapons
With the testing of the first nuclear weapon (Trinity on July 16, 1945) it became clear that seismometers could record the vibrations created by such devices
Trinity was detonated in New Mexico, on a tower about 50 ft high, and yet it was seismically recorded hundreds of kilometers away (in St. Louis!)
Introduction to Seismology

17. Seismology and Nuclear Weapons
Thus, there existed the possibility of using seismic data to tell when a nation had detonated a nuclear device and how much energy it had released.
Throughout the 1950’s it became increasingly clear that aboveground nuclear explosions caused significant environmental contamination
Introduction to Seismology

18. Seismology and Nuclear Weapons
Ultimately this led to the signing of the Limited Test Ban Treaty that outlawed all aboveground weapons testing.
With only buried tests being conducted, other detection methods such as infrasound, hydroacoustic, and electromagnetic monitoring, became less effective, making seismology more important.
Introduction to Seismology

19. Seismology and Nuclear Weapons
This spawned the first global network of uniform high quality seismometers.
This network was known as the World Wide Standard Seismograph Network (WWSSN).
It was upgraded to form the Global Seismic Network (GSN) with modern instruments in 80’s
Verification seismology remains just as important today as it was during the arms race between the Soviets and the US in the 1960s and 1970s
Introduction to Seismology

20. Seismology and Nuclear Weapons
Introduction to Seismology

21. Seismology and Nuclear Weapons
Introduction to Seismology

22. Seismology and Nuclear Weapons
Introduction to Seismology