Wood–Anderson seismometer

In 1908, geologist Grove K. Gilbert paid Harry Wood $1,000 to draft a map of potentially active faults in northern California and several years later Andrew Lawson, professor at the University of California, Berkeley assigned Wood to oversee the University's seismometers, where attention was focused on local earthquakes as well as the distant events that were used (especially by European scientists like Beno Gutenberg) to study the attributes of the Earth's interior.

He would serve as Wood's mentor who took his advice and went to work at the Bureau of Standards in Washington D. C. where a relationship was developed with George Ellery Hale, the director of Carnegie's Mount Wilson Observatory in Pasadena.

[3][4] In March 1921, the Carnegie Institution accepted a proposal from Wood to provide financing for a long-duration program of seismological research in Southern California.

As a researcher for the Institute, Wood worked in a partnership with John A. Anderson (an instrument designer and astrophysicist from the Mount Wilson Observatory) to pursue the development of a seismometer that could record the short-period waves from local earthquakes.

Their instrument would require the ability to measure the seismic waves with periods from .5–2.0 seconds, which were considerably shorter than what the existing units were able to detect.

In September 1923, with the successful completion of what became known as the Wood-Anderson torsion seismometer, the focus became establishing a network of the instruments throughout the region that would be able to pinpoint earthquake epicenters and eventually allow mapping of the corresponding fault zones.

[9] Richter resolved some difficulties with this method[10] and then, using data collected by his colleague Beno Gutenberg, he produced similar curves, confirming that they could be used to compare the relative magnitudes of different earthquakes.

The scale was calibrated by defining a magnitude 0 shock as one that produces (at a distance of 100 km (62 mi)) a maximum amplitude of 1 micron (1 μm, or 0.001 millimeters) on a seismogram recorded by a Wood-Anderson torsion seismometer.