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California Earthquakes Disrupted HF Propagation on West Coast

From: ARRL.org

British Columbia radio amateur Alex Schwarz, VE7DXW, said that an Independence Day magnitude 6.4 earthquake in California’s Mojave Desert and multiple aftershocks negatively affected HF propagation on the US west coast. Schwarz, who maintains the “RF Seismograph” and has drawn a correlation between earthquake activity and HF band conditions, said the radio disruption began at around 1600 UTC on July 4, and continued into July 5. He said that on July 4, the blackout was total except for 20 meters, where conditions were “severely attenuated,” Schwarz said. The RF Seismograph also detected the magnitude 7.1 earthquake on July 6 in the same vicinity, Schwarz reported. The distance between the monitoring station in Vancouver, British Columbia, and that quake’s epicenter is 1,240 miles.

“Things are back to normal after the strong quake, as far as the ionosphere is concerned, but the unrest has not stopped yet,” Schwarz told ARRL on July 8. “There were over 7,000 mostly small quakes, and these do not seem to have the energy to effect the ionosphere. We all hope that this will settle down soon.” Schwarz said the RF Seismometer detected a magnitude 6.9 earthquake in Indonesia.

Over the holiday weekend, Schwarz had reported “a massive short-wave radio blackout” on the west coast. “It is not caused by the sun (the sun is quiet), but the field lines of the ’quakes themselves,” he said. A magnitude 6.2 earthquake took place off Vancouver Island, British Columbia, on July 4.

On July 6, Schwarz said, the RF Seismograph showed an increase in noise on 80 meters some 13 hours beforehand, as well as some propagation changes on 40 and 30 meters — low before the quake and increasing in its wake. Increases in noise on 15 and 10 meters were detected some 10 hours before the earthquake, diminishing about 3 hours afterward. In addition, noise level and propagation changes on 20 meters some 3 hours before the earthquake.

Schwarz said larger quakes spur longer periods of 80-meter noise which cross the day/night boundary. “The difficulty is the 80 meter noise difference between day and night, which is hard to subtract from the graphs,” he added. With earthquakes of lesser magnitude (4.0 to 5.9), the RF Seismograph displays the rise and fall typically within daytime or nighttime propagation, making it more obvious. “The measurement on the other bands is more consistent, and the quake can have either an amplifying or attenuating effect on propagation,” Schwarz told ARRL.

All of the earthquakes of the past few days occurred within a 4-square-mile area in and around Ridgecrest in San Bernardino County. Several injuries were reported, along with property damage. ARES and the Sierra Amateur Radio Club (SARC) have actively supported communications during the earthquake swarm and magnitude 7.1 quake in and around Ridgecrest, in the Mojave Desert. “Many club members are busy collecting information, running an emergency net, as well as staffing a back-up communication van,” Mike Herr, WA6ARA, told ARRL on July 7. 

The RF Seismograph propagation tool employs an omnidirectional multiband antenna to monitor JT65 frequencies (±10 kHz) on 80, 40, 30, 20, 15, and 10 meters. Recorders monitor the background noise and display the result in six color-coded, long-duration graphs displaying 6 hours of scans. When signals are present on a band, its graph trace starts to resemble a series of vertical bars. 

The RF Seismograph recorded the magnitude 7.5 earthquake in Ecuador on February 22. Schwarz recounted that noise on 15 meters began to be visible about 1 hour before the quake; then, 2 hours after the quake released, 15 meters started to recover. It did not affect 80 meters. “The earthquakes show up as RF noise because of the electric field lines, now scientifically confirmed to change the way the ionosphere reflects RF,” Schwarz said.

Schwarz has cited an article in the October 2018 edition of Scientific American, which, he says, explains the phenomenon. (See Erik Vance’s “Earthquakes in the sky,” Scientific American, October 2018, p. 44.)

The Scientific American article explores measurements in Japan and how earthquakes can create electric field lines that extend into the atmosphere. Schwarz said 171 earthquakes — all magnitude 6.0 events or greater — were studied, and only 15 of them had no RF noise associated with them. 

RF Seismograph is now a project on Scistarter.com, facilitated through Arizona State University. Contact Schwarz for additional information.

Written by

Canadian amateur radio operator since 2007. Operating on the VHF/UHF bands and local repeaters in the Durham Region area. Husband and the father of four.

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