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posted by chromas on Tuesday November 20 2018, @05:36PM   Printer-friendly

Phys.org:

World War II-era oil pumping under Los Angeles likely triggered a rash of mid-sized earthquakes in the 1930s and 1940s, potentially leading seismologists to overestimate the earthquake potential in the region, according to new research published in AGU's Journal of Geophysical Research: Solid Earth.

Six independent earthquakes and two aftershocks of magnitude 4.4 to 5.1 shook L.A. between 1935 and 1944, a rate of about one every two years. The area also experienced a higher rate of low-intensity earthquakes during that time frame. After 1945, the rate dropped to one moderate earthquake every seven years.

The new study re-examined historical information about the earthquakes from archived newspaper reports of earthquake damage, postcard questionnaires collected by the Coast and Geodetic Survey, and other sources pulled from old files and the dusty corners of cyberspace.

The authors used this information to refine the earthquake locations identified by early earth-motion sensors. The first seismometers in the United States began monitoring earthquake activity in the L.A. region in 1932. It is known that these early instruments could err in locating earthquake epicenters by tens of miles because of the limitations of their clocks, and because the low-sensitivity instruments were so few, according to the study's authors. Extrapolation of earthquake location from seismometer recordings relies on accurate time measurements.

The oil companies active at the time associated their activities with increased earthquakes, because the quakes would often sever pipes and shutdown production for months.


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  • (Score: 1) by khallow on Wednesday November 21 2018, @01:42PM

    by khallow (3766) Subscriber Badge on Wednesday November 21 2018, @01:42PM (#764698) Journal

    I was pointing out that releasing the same amount of deformation tension can result in orders of magnitude difference in the energy involved depending on how you do it.

    Even using the ideal spring law, you have ten times the tension at the point of release for a 10 cm displacement. And said tension is not linear over time precisely because of the potential energy build up required.