Earthquakes and California
Chapman University – ESCU 234
Lecture 1 – A Brief History of
Earthquakes and Seismology
• In the last 500 years, more than 7
million people have died from
earthquakes and many more have
seen their food sources and local
• In the 20th century alone, earthquakes
have caused over 50% of deaths
caused by natural disasters
• The hazard that earthquakes present
to a growing population is often the
primary concern of scientists and
Yet earthquakes have also proven to be a great source of
geologic knowledge :
- structure of earth’s interior
- composition of earth’s interior
Seismology, the scientific study of earthquakes, is an
extraordinarily young science – only about 100 years.
Although people have speculated about the causes of
earthquakes for 1,000’s of years.
The Earliest Records
• The oldest written records of earthquakes have
been traced back to 1831 B.C. in the Shandong
Province of China. The record states merely of
the “shaking of Taishan Mountain”.
• But the record is fairly complete only from 780
• Some historical reports are so detailed that from
them, modern studies have been able to establish
the distribution of damage and the size of the
• On September 2, 1679, the greatest known earthquake near
Beijing, China, was mentioned in the records of 121 cities.
When modern researchers compared the descriptions of
building damage, ground cracks and other features near the
source together with reports of shaking, with recent
earthquakes, they concluded it was similar to the 1906 San
Francisco earthquake (magnitude 7.9).
• Despite their careful documentation, Chinese scholars were
unable to achieve any insight into the causes of the
catastrophic ground shaking
• It was thought that earthquakes and
other natural disasters were caused
by supernatural forces such as the
Early Greek Ideas
• Thales 580 B.C. believed that movements
of water produced earthquakes
• Anaximenes 526 B.C. believed that
Earth’s interior was hollow and rocks
falling in the interior would strike other
rocks causing vibrations
• Anaxagoras 426 B.C. viewed fire as the
cause of at least some earthquakes
• Seneca A.D. 63 believed that earthquakes
were caused by air finding its way into
Aristotle 384-322 B.C.
• Like many of his contemporaries was convinced
of a “central fire” inside the earth. The fire would
rise and if obstructed would burst violently
causing vibrations and noise
• A later modification suggested that these
subterranean fires would burn away supports of
the outer parts of the Earth. The ensuing collapse
would create earthquakes.
• Although incorrect, his ideas were widely
accepted until the 18th century.
• Other important observations of Aristotle:
– Different types of quakes based on shaking was
mainly vertical or diagonal
– Whether quake was associated with vapors
– Places where subsoil is poor are shaken more
because of the large amount of “wind” they absorb
A new era dawned in the 18th century under
the influence of Sir Isaac Newton’s writings
of waves and mechanics. His laws of motion
provided the physical theory needed to
explain earthquake waves.
Sir Isaac Newton
1750 is often referred to as the “year of the earthquakes” because
London, England was jolted by earthquakes several times. Still and many
writers showed, earthquakes were usually believed to caused by either
supernatural causes or causes hypothesized by the Greek scholars of long ago.
In fact, a writer in a scientific journal apologized “to those who are apt to be
offended by any attempts to give a natural account of earthquakes”.
The Lisbon Earthquake of 1755
The scientific study of earthquakes received an important
boost in 1755 when a disastrous earthquake struck in the
Atlantic Ocean, several hundred kilometers south-
southwest of Portugal on November 1st.
• 60,000 + residents of Lisbon were killed
• ocean waves 30-40 above high tide level swamped
• fires burned for 3 days
The Lisbon earthquake of 1755 was a major source of
inspiration for one of the first modern “Fathers of
Seismology”, the British engineer John Michell (1724-1793).
In his description of the earthquake written in 1760, he
classified two types of earthquake waves:
• A tremulous vibration; followed by,
• Wavelike undulation of the Earth’s surface
Michell also concluded
that the speed of
earthquake waves could
actually be measured
from their arrival times
at two different points.
accounts he calculated
that the waves in the
traveled about 500
meters per second (m/s).
Although incorrect, it
was the first attempt at
such a calculation.
Robert Mallet and the Great Italian
Earthquake of 1857
The earthquake of December 16, 1857
near Naples in southern Italy provided
Robert Mallet the opportunity to study
seismic effects extensively and lay a
firm foundation for modern seismology.
Mallet did much to further the
interaction between engineering,
geology, and mechanics. His goal was
to take earthquake studies from a stage
of mystery by applying physical and
engineering principles to the search for
the real nature of earthquakes.
• In Mallet’s landmark work “The First Principles of Observational
Seismology” he coined much of the basic vocabulary describing
earthquakes that we still use.
• Mallet is also notable for being the first to work with artificial
earthquakes. He exploded charges of gunpowder underground, then
recorded the waves by watching the surface of a container of mercury
placed at a distance from the charge. A stopwatch gave him the
elapsed time between the explosion and ripples on the mercury
• From these observations he deduced that earthquake waves travel at
different speeds through different materials. For the first time it was
clearly understood that seismic waves are affected by the physical
properties of the different rocks through which they pass.
- sandy soil 280 m/s
- granite 600 m/s (Too small!)
• Believing that earthquakes such as that which struck Naples were
produced by volcanic sources, he drew attention to the nearness of
volcanoes such as Mt. Vesuvius to the area. From his notion of an
explosive source (which is wrong!), Mallet inferred correctly that the
seismic waves would start at a point, the focus or hypocenter.
• Further, he suggested that seismic waves resembled sound waves
traveling in the air. From this he concluded that the first motion of the
ground would show a regular direction away from the initiation point.
objects thrown from heights
directions of cracks in buildings
To calculate the position of a hypocenter.
• Based on his studies, Mallet calculated the depth of the Naples
earthquake to 6 ½ miles beneath the surface.
Knowing what we do today about earthquakes and seismology,
Mallet’s methods were impractical. Nevertheless, this was the
first attempt to estimate the origin of an earthquakes motion.
Not until 50 years later with the development of the modern
seismograph could earthquake hypocentral depths be calculated
(and still not all that well today!).
Four Key Earthquakes
In the mid to late 1800’s two organizations were created that
contributed much to the science of earthquakes
- 1857 Geological Survey of India
- 1879 United States Geological Survey
An early work of the USGS was done by M. L. Fuller in 1912
who published evidence on three extraordinarily large shocks
which occurred along the Mississippi River
- December 16, 1811
- January 23, 1812
- February 7, 1812 (reportedly the largest)
• All together, over 1870 earthquakes shook the area between December 16 and
March 16. Eight of these were severe, felt in Louisville, Kentucky, 200 miles
• Damage occurred over 30,000 to 50,000 square miles bordering the
Mississippi River southward from New Madrid, Missouri.
• The largest of these shocks awakened President Madison in the White House
rang church bells in Boston, Massachusetts, and toppled chimneys in Cincinnati,
Significance: At the time, it was a geological puzzle why such immense
earthquake energy was released in a continental interior. Earthquakes were
always considered to occur on the edges of continents.
On June 12, 1897 another very important event struck the province of Assam in
northeast India. As reported by Richard D. Oldham, head of the Indian Geological
• The earthquake was felt over an area of 1 ¾ million square
• Completely devastated 9,000 square miles
• Fewer than 1,000 people died because of low population
density and few large structures
• Shaking (strong) lasted about one minute
• Persons were thrown to the ground R. D. Oldham
• Powerful accelerations of the ground threw boulders straight
• Sandy soils behaved as a liquid and reported homes sinking
until only the roof was visible
• Oldham reported that in heavily shaken areas, people saw
visible waves (~ 1 ft. high) moving across the ground
• Vertical throw of 35 feet along a deep “thrust” fault
The Contribution of the 1906 San Francisco Earthquake
The turning point in our understanding of
the causes of earthquakes came from the
studies of the earthquake that shook central
and northern California on April 18, 1906.
• No active volcanoes nearby, therefore geologists were not
tempted to turn to old Greek notions
• Source of the 1906 earthquake lay beneath a readily traversed
area that surveyors had already covered with survey markers
showing distances and relative heights between points (note that
these were not available in either the 1811-1812 and 1897
• This allowed mapping of the ground deformation
To study the quake the “State Earthquake
Investigation Commission” was set up
under University of California, Berkeley
professor Andrew Lawson. Scientists
assembled under Lawson compared
geodetic measurements prior to and after the
Their report contained the fundamental
theory that has dominated seismology to this
day. The report concluded that the severe
ground shaking had been generated by
The San Andreas fault south of San
sudden slip on what Lawson called the San Francisco following the 1906 earthquake.
Andreas Fault. The fault had slipped over a
section extending for more than 400 km
from San Juan Bautista south of San
Francisco Bay to a point ~ 250 km north of
The Japanese Earthquake of 1923
By the 1920’s scientists were looking for
patterns in seismic events that might point to the
location of future earthquakes. Dr. Fusukichi
Omori, Director of the Seismological Institute
of Japan had been studying the apparent
distribution of large earthquakes in the vicinity
of Honshu. In 1922 Omori wrote that the
vicinity near Tokyo was seismically quiet but
that regions ~ 60 km away it were active (this is
called a seismic gap). Thus he felt the area was
due for a particularly devastating earthquake.
Approximately one year after his prediction, on
September 1, 1923 at about noon when the
streets of Tokyo were filled with people, a
particularly devastating quake hit, the Kwanto
Devastation along Ningyocko St., Tokyo Seismogram from Kwanto
Refugees in front of the Imperial Palace
Damage at Miyamachi Tagaata-gun Shiuoka-ken following the 1923 earthquake