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First "Seismoscope" Invented
The first seisomoscope ever invented was in 132 A.D. by Chang Heng in China. These differ from seismographs, for they show only qualitative data for seismic activity. -
Lisbon Earthquake
The Lisbon Earthquake is often considered to mark the dawn of modern seismology. It was a basis for theories of wave propagation, and its widespread effects led to a pique in scientific interest over earthquakes. -
Theory of Elastic Wave Propagation
This theory was developed by several people, including, Caucy, Poisson, Stokes, and Rayleigh, in the beginning of the 1800s. It describes that there are essentially 2 main groups of seismic waves: surface waves and body waves. Surface waves are called so because their motion is restricted to near Earth's surface. Body waves are divided into primary (P) waves, or secondary (S) waves. P waves travel in a "push-pull" manner, whereas S waves are "shake" waves. -
First Attempt at Observational Seismology
Robert Mallet, an Irish geophysicist and civil engineer, often thought of as the founder of modern seismology, studied an earthquake that occurred near Naples, Italy. His observations led to the idea that earthquake waves radiate from a central focus, and he determined that more must be done to monitor earthquakes. -
First Seismograph
Filippo Cecchi builds a low sensitivity and the first time-recording seismograph in Italy. It's the highest quality earthquake measuring instrument to date, but it's still not very accurate. -
First Seismograph in North America
The first seismograph was installed in Lick Observatory close to San Jose, California. This same instrument later recorded the 1906 San Francisco earthquake. -
First Seismometer with Damping
Emil Weichert used viscous damping to create a seismometer that could measure earthquake energy for the entirety of the earthquake. It was the first instrument capable of producing a record that was actually useful for the duration of the ground shaking. -
First Electromagnetic Seismograph
B.B. Galitzen developed the first electromagnetic seismograph, in which a moving pendulum was used to generate electric current in a coil. It proved to be much more accurate than earlier mechanical instruments, and nowadays, all seismographs are electromagnetic. -
Elastic Rebound Theory
H. F. Reid, American engineer, studies survey lines across the San Andreas fault measured before and after the 1906 earthquake. His elastic rebound theory proposes that the origin of an earthquake is caused because of accumulated elastic energy that is suddenly released by slip on the fault. -
Richard Oldham
Richard Oldham identified P, S, and surface waves in earthquake records. From the absence of waves at certain distances, he was able to confirm the existence of Earth's core. -
The Moho
Andrija Mohorovicic discovered what was later named the "Moho." It is a velocity boundary between Earth's crust and mantle that was identified after meticulous analysis of seismic data near the Kulpa Valley earthquake, which occurred in Croatia. -
Travel Time Tables
Though the first comprehensive time tables were produced by Zoppritz in 1907, Beno Gutenberg publishes travel times for core penetration and reflection. His travel-time tables include core phases, which are seismic waves that penetrate or reflect from the core. They also accurately estimate the depth of the Earth's fluid core. -
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1920s
More advanced seismic surveying methods are developed in the US. These new methods use explosions and artificial sources to explore for oil and any other natural resources in Earth's shallow crust. -
Richter Scale Invented
Charles Richter developed a magnitude scale in 1935 as a mathematical device that would compare the size of earthquakes, focused mainly on those in southern California. It's logarithmic and allows for a large range of earthquake sizes to be measured. -
Earth's Solid Inner Core
I. Lehmann discovers the Earth's solid inner core, introducing the "I" phase. -
Jeffreys-Bullen Seismological Tables
H. Jeffreys and K. Bullen publish final versions of their travel time tables. They use large volumes of data and improved analysis of epicenter locations to derive new standard earth model. These are so accurate that they are still in use today. -
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The Cold War
The Cold War, specifically during the 1950s and 1960s, had a large effect on seismology. Funding for seismology programs surged because the US wanted to know more about the Soviet nuclear tests being conducted in the early 1950s. Lots of new seismologic technology and advancements resulted from this time. -
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1960s
Chilean Earthquake of 1960 promotes new research, for its records allow scientists to study Earth's free oscillations and normal modes. Computer application in seismology also starts to become more popular during this time. It's discovered that earthquakes are concentrated in narrow belts around the globe. The plate tectonics theory is validated by evidence of earthquakes located along dipping zones and that "focal mechanisms" are inferred from spatial patterns of radiated energy. -
WWSSN Established
The Worldwide Standardized Seismograph Network was established in 1961 and consisted of well-calibrated short and long-period seismographs. It contributed to many advances in seismology, but it would later be replaced by the GSN. -
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1970s
In the 1970s, the first digital global seismographs are installed. The first digital portable seismographs also begin to be used for special studies, and the centralized archives of digital seismic data is established. -
GSN is Created
The US National Science Foundation and US Geological Survey provide funding for a new, digital seismic network known as the GSN, or Global Seismographic Network.
