The Great San Francisco Earthquake: A Mini-Unit

In 1906 a sudden and unexpected event occurred: the Great San Francisco Earthquake. The city was severely damaged by the magnitude eight earthquake along the San Andreas Fault, felt as far away as Oregon. Even more destructive was the resulting fire caused by broken gas pipelines which exploded, burning nearly all the remaining city. If that wasn’t enough, all the waterlines had also been broken by the earthquake, and it was only by blasting some of the remaining houses that the fire was brought under control by the resulting firebreak.

The study of earthquakes was hardly advanced at that time, and many new and undiscovered principles and effects of earthquakes have since been discovered by those investigating the causes of the San Francisco earthquake and destruction. Indeed, the predecessor of the now popular plate tectonics theory was spawned by this event. Fences around the San Francisco area had been broken in two by the earthquake. The pieces had been moved around in such a way that the boundaries of property in the area were difficult to discern. Attempts at surveying the damage led H. F. Reid, a scientist of the time, to propose that the earth’s crust was stretching like a rubber band, and that earthquakes were caused when the stretching became “stuck,” and then finally broke free. The trouble was, he couldn’t explain what would cause the stretching to stick.

After continuing the survey of California, scientists produced so much evidence of movement, that the now common plate tectonics theory was proposed. Plate tectonics explains that earthquakes can occur as the earth’s plates are moving. When one jagged edge of a plate snags on another, both plates stop moving. This causes pressure to build up until the plates break free. Result? Built up force is released at once, making the ground move. This theory underlies the world’s understanding of earthquakes today.

Another interesting effect of earthquakes that was noticed during the San Francisco earthquake was liquefaction. In liquefaction, wet sandy ground, which is ordinarily a good foundation for buildings, is shaken and the water in it is, in effect, squeezed out due to the pressure waves of the earthquake. The sand then turns into a muddy liquid and flows, causing buildings to sink into it and collapse, and as was the case in the 1906 earthquake, the flow snaps waterlines needed to fight fires. So much for good sandy foundations.

The large 1906 earthquake contributed greatly to science by helping unveil the chief scientific explanation of why the ground moves. San Francisco was rebuilt on a much larger scale than ever before with more earthquake-resistant buildings. New building codes were enacted, such as cross bracing in walls, and setting buildings on shock absorbing foundations. In short, the Great San Francisco earthquake of 1906 contributed the concept of plate tectonics to earthquake science and has left San Francisco in readiness for the next big quake.

Further Investigation

San Francisco Earthquake and Fire April 18, 1906
This grainy video is among the earliest known footage of the disaster.

The Great 1906 San Francisco Earthquake
Background information from the U.S. Geological Survey (USGS). Use the sidebar on the left to navigate.

Timeline of the San Francisco Earthquake: April 18-23, 1906
A chronology from the Museum of the City of San Francisco.

April 18, 1906
Eyewitness account from the son of a battalion chief in the San Francisco Fire Department.

The Call = Chronicle = Examiner April 19, 1906
Newspaper front page from the Library of Congress.

San Francisco Earthquake 1906
Images from the Library of Congress starting with Union Square pre-quake.

The California Earthquake of April 18, 1906
A variety of images showing displacements and flows.

USGS Report on the San Francisco Earthquake 1906
Maps and photos.

100 Years after the 1906 Earthquake
Award-winning 46-minute video from the USGS with historical footage and interviews.

Facing the Great Disaster
18-page .pdf download from the USGS subtitled, How the Men and Women of the U.S. Geological Survey Responded to the 1906 “San Francisco Earthquake.”

People, Land and Water – April, 2006
Very informative, 36-page, 100 anniversary edition detailing 1906 earthquake.

1906 Quake Launches Modern Earthquake Science
PBS NewsHour in-depth coverage on the 100th anniversary discussing the advances resulting from the quake.

The California Earthquake of April 18, 1906
The most comprehensive investigation, known as the Lawson Report. Probably too comprehensive for most, but interesting nevertheless.

The Science of Earthquakes
Simple earthquake science covering the different types of faults and how they are measured. From USGS.

Earthquake Facts
Interesting facts from USGS.

Earthquake Science Explained
18-page download for young people.

Activities

Earthquake Glossary
Interactive glossary from USGS.

Will This Building Stand?
Interactive multimedia comparing four types of buildings in various earthquake magnitude scenarios.

The Restless Planet: Earthquakes
Animation of an earthquake as it travels. From PBS.

Real-Time Earthquake Map
They are occurring more often that you might think!

Liquification Activity
“What happens to sandy or fine-grained soils when an earthquake shakes them up? Try this simple activity to find out.”

The Principles of Earthquakes
Papercraft demonstration from Canon.

Edible Experiments
What is more fun than edible experiments?

Graham Cracker Earthquake for the younger student
Candy Quakes for the older student.

How Many Earthquakes Does it Take to Build a Mountain?
Experiment for older students with a geometry and trigonometry background. From JPL.

How Much Bigger…Calculator
An interactive calculator that compares earthquake magnitudes.

Books

The San Francisco Calamity By Earthquake and Fire by Charles Morris
This book now in the public domain is largely a compilation of eyewitness accounts.

If You Lived At The Time Of The Great San Francisco Earthquake by Ellen Levine
Some homeschoolers like (and some greatly dislike) the books in this series published by Scholastic. The choice, as always, is up to you!