FYI: That 3.4M San Francisco Earthquake Was (Probably) on the San Andreas Fault Zone

San Francisco residents were tossed into a fit of panic today when the ground beneath them started shaking… from a small earthquake (likely) along the most famous seismic fault line in the world.

Today, February 2nd, a preliminary, which has now been elevated to a 3.4 magnitude tremor — up from its original 3.2 magnitude estimate — struck off the coast of San Francisco sometime around 1:32 p.m., according to the United States Geological Survey (USGS).

The earthquake, itself, caused nervous shock and ground trembling that could be felt across the city, as well as into the East Bay, Peninsula, and up toward Novato. Per the USGS, the seismic vibrations registered as “light” shakings, incapable of causing damage — a fact later confirmed by the San Francisco Fire Department on social media, citing that the department didn’t receive any reports of damage from the quake.

(Earlier today, the USGS also reported another earthquake off the Northern California coast; the much larger 4.9 magnitude earthquake struck at 7:09 a.m., about 70 miles off the coast of Eureka.)

Multiple news outlets reported San Francisco residents felt the tremor… with some thankful that their emergency earthquake kits were well-stocked and up-to-date. Thankfully, none were needed… though today’s tremor served as a sobering reminder that we’re on borrowed time, and we should all make sure our kits are prepared accordingly. Or… you know… make one to begin with.

But what was just as fascinating and, ostensibly, chilling about today’s San Francisco earthquake is that if you look at its epicenter, there’s no denying it occurred on the San Andreas Fault line.

In the USGS’s most recent overview report for the tremor, the government agency lists its epicenter at 37.713° North, 122.552° West. The middle coordinates for the San Andreas Fault zone, which runs 800 miles long at a depth of at least 10 miles throughout much of its system? 35.1361, North, 119.6756° West.

That puts today’s quake directly, or near as much, along the San Andreas fault system. Even without knowing the exact longitudinal and latitudinal coordinates of today’s San Francisco earthquake, comparing side-by-side pictures of the San Andreas Fault zone along with the USGS’s interactive map for the tremor shows an undeniable overlap.

Now don’t go about doom-watching 2015’s San Andreas for despondent effect — (I mean, I know most of us during the dark days of the COVID-19 lockdown watched Contagion at least once; lesson learned, don’t scratch similar itches) — because there’s no alarm for concern. The spots along the San Andreas Fault zone produce thousands of small earthquakes each year, with many of those with the same magnitude as today.

What made the February 2nd quake so spectacularly newsworthy was its proximity to San Francisco; the USGS used the San Francisco Zoo as its proximity index, for context.

Now… about that earthquake emergency kit.

Related