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.