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An Earth Mover

On April 18, 1906, the most destructive earthquake in US history devastated much of San Francisco. This event, approximately 8.0 on the yet-to-be-invented Richter scale, occurred along the San Andreas Fault, a tectonic plate boundary from which the Earth’s crust spreads horizontally as the North American Plate moves Southwest and the Pacific Plate moves Northwest.

Earthquake research and observation in the U.S. had lagged behind Europe and Japan until the San Francisco event On This Day. When this 1906 earthquake struck, California-based scientists began to assemble observations of the earthquake and its effects.

Observations and data were compiled and published in 1908, in The California earthquake of April 18, 1906: report of the State Earthquake Investigation Commission, in two volumes and atlas. Generally called the “Lawson Report” after Professor Andrew C. Lawson, Geology Chair, University of California, Berkeley, who headed the Commission, it became a benchmark for investigations into earthquakes effects. The report included detail on damage, San Andreas Fault movement, seismograph records of the earthquake from around the world, photographs, maps, and up-to-date information about the underlying California geology. In the U.S., Seismology and other Earth Sciences began their rapid growth from that moment.

Today, well over 100 years later, we can track some plate movement through ground-based measurements using laser-electronic equipment and through the new science of space geodesy using space-based measurements from very long baseline interferometry (VLBI), satellite laser ranging (SLR), and GPS. On the ground, instruments sensitive to special aspects of the ground’s features are reflected in their names – magnetometers, creepmeters, deep borehole pore pressure monitors, crustal strainmeters, and tiltmeters.

Although we have learned much since 1906 about this fault, we have much more to learn about how the Earth’s crust moves.

B Bondar / Real World Content Advantage