Supersonic Aircraft Tracked Off San Diego Coincided With Mysterious "Skyquake"

There are strong indications that a mysterious boom heard in and around San Diego was from a supersonic aircraft on a training mission off the coast.

A satellite image of the South California coastline.
Google Earth

Residents of San Diego County in South California, as well as other nearby areas, heard and felt at least one loud boom late yesterday. The U.S. Geological Survey did not detect any earthquake activity at the time of this incident, which occurred at around 8:20 PM local time on June 8th, 2021, and that some are referring to as a "skyquake." There are strong indications that this was a sonic boom and flight tracking data available online does show an unidentified plane flying at supersonic speeds off the coast in a general area that regularly hosts military training exercises, among other military aviation activity, at around the same time. A U.S. Navy supercarrier was also training in the area yesterday.

The San Diego Union-Tribune has reported that people were talking about hearing and feeling the boom in areas as far east as El Cajon, a city in San Diego County, around 17 miles inland from the Pacific coastline, and as far as south as Tijuana, just over the border in Mexico. KMFB-TV, a local CBS affiliate in San Diego, said that the U.S. Geological Survey (USGS) had recorded a minor earthquake, which is not common in the region, at around 5:37 PM local time, but nothing at around 8:20 PM.

ADS-B Exchange

Online flight tracking software recorded the following route, which was taken by an aircraft flying at supersonic speeds around the time of the reported "skyquake" on June 8, 2021. The dashed line seen heading off toward the northeast is actually a gap in the data and connects to an unrelated track in France.

Sonic booms are hardly unheard of in the area. There are a number of formalized U.S. military test and training areas off the coast of San Diego, as well as further to the north toward Los Angeles, where fast-flying fighter jets often operate and where high-speed flight testing, including of hypersonic vehicles, has taken place in the past. 

The Navy, in particular, also regularly conducts training in parts of the Pacific just off the coast of Mexico's Baja Peninsula. This includes workups for aircraft carrier strike groups, including their air wings, ahead of deployments. In addition to the fighter jets flying from these carriers' decks, these exercises can involve contractor-operated and military "red air" aggressor jets that are also capable of hitting supersonic speeds. This often includes these adversaries flying supersonic profiles meant to simulate incoming cruise missiles.

It's certainly important to also note that the Nimitz class carrier USS Carl Vinson was operating in the area yesterday. The ship had left San Diego two days earlier and returned off the coast today.

Online flight tracking data available through ADS-B Exchange shows an unidentified aircraft flying off the coast of San Diego, as well as Baja, at altitudes between 20,000 and 25,000 feet, last night. The data shows a recorded speed of 967 knots at 8:27 PM, certainly fast enough to produce a sonic boom at the altitudes in question. The proximity of the track to the shore also lends credence to the boom and associated shockwave being heard and felt across the San Diego County Area. 

The transponder broadcasting that information appears to have been miscoded and the code in question, 249249, has been associated with various aircraft in the past, including types not capable of supersonic flight. As such, it does not offer any obvious clues as to the type of aircraft, or who may have been operating it, recorded off the coast of Southern California last night. 

The track itself is very similar to what we see from aggressor jets that fly against U.S. Navy ships in the area regularly. You can see examples of this in great detail here. The difference being, in this case, the track was offset closer to the Baja Peninsula than normal. Generally, the military aggressors are not trackable and a miscoded transponder is not very suspicious regardless. Contractor aggressors usually are trackable, at least for certain portions of their flight.

Tyler Rogoway

F-21 Kfir and Mk58 Hawker Hunters from ATAC that often play adersary for Navy ships training in the SoCal range complex. The F-21s are supersonic capable. Navy aggressors and test fighters also take part in these exercises. 

The beginning of the track also seems to indicate that the aircraft in question took off from Naval Air Station North Island, part of Naval Base Coronado in San Diego, which is where high-performance military aggressors working in the area typically operate from, as well as a number of contractor aggressors. The War Zone has already reached out to the public affairs office at Naval Base Coronado for more information.

Separately, a public affairs officer at Marine Corps Air Station Miramar, which is situated some 12 miles northeast of downtown San Diego, told The War Zone that the only aircraft flying from that base at the time "were KC-130s, and they are definitely not producing a sonic boom sound." 

The Miramar public affairs office also directed The War Zone to contact Camp Pendleton, another Marine Corps base further to the northwest, where artillery training has been going on this week. "Depending on atmospheric conditions, the sound of the explosions may be amplified and heard up to 50 miles away. Although we cannot account for every loud noise heard in Southern California, what you are hearing may be a result of our training," a public affairs officer at Camp Pendleton told us in a separate statement.

However, it seems unlikely that artillery fire, even if it was audible across a broad area, would have caused the earthquake-like shaking felt across so much of San Diego County and adjacent areas. The reported incident last night would seem overly brief to have been associated with training involving either howitzers or rocket artillery systems, where multiple rounds are generally fired in succession, as well.

The video below shows Marines training with 155mm M777 howitzers at Camp Pendleton in 2013, including the firing of multiple rounds in succession.

A spokesperson for Naval Air Facility El Centro, which is located around 85 miles east of San Diego, also told The War Zone that "we do have squadrons come out here for detachment and training," but "currently, there are no fixed wing aircraft at the installation." They added that "operations over the San Diego area are outside of our controlled airspace and we do not have the means to monitor that area."

When reached for comment, a public affairs officer at Vandenberg Space Force Base, situated northwest of Los Angeles, said they had no information about the incident to the south and were not even aware that it had happened. Vandenberg regularly supports missile tests and space launches, among other activities

However, missile and space launches from that base typically prompt the issuing of warning notices to airmen and mariners for certain dates. There do not appear to have been any such notices issued for June 8th with relation to Vandenberg, though there are ones active for upcoming planned launch events later this month, as seen in the Tweets below.

The War Zone contacted a number of other U.S. military facilities in the region, and the Federal Aviation Administration (FAA), about the "skyquake," as well. 

We have also sent out inquiries about two other as-yet-unexplained "skyquakes" that residents of the San Diego County area experienced earlier this year, on February 16 and March 10, respectively. It is, of course, important to note that there are no indications one way or another that any of these incidents are necessarily linked to each other.

That being said, the public affairs officer at Miramar told The War Zone said that F/A-18 Hornet fighters were flying from their base on February 16, but that they had landed well before the reported boom and associated shaking. Similarly, on March 10, the only flight activity at Miramar was the departure of a pair of F-35 Joint Strike Fighters nearly an hour after reports of the incident that day had emerged. 

Unexplained sonic booms, as well as other rumblings in the sky, are not new to California, either. There was a particular surge of such reports in the state in the 1990s, leading to speculation that they could be related to top-secret aircraft capable of flying at extreme speeds.

Whatever the case, people living in San Diego County and surrounding areas have certainly been experiencing something. 

"Yes, I heard it. No, I don’t know what it was," San Diego Mayor Todd Gloria wrote on Twitter after the most recent episode. "I’ll share if I get any information."

Given the presence of Carl Vinson in the area at the time, the familiar track, and its close proximity to the shore, in this case, it sure looks like the culprit of the boom was a normal adversary supersonic profile flown at a Navy ship, likely part of a carrier strike group undergoing routine training.

We will also certainly continue to update this story as more information becomes available.

Contact the author: joe@thedrive.com