Locals described their homes being shaken and their hearts racing as the quake struck. The epicentre was in the Ashland neighbourhood on the outskirts of San Leandro, and it hit about 6:30 p.m.
The earthquake’s intensity rating dropped from 4.2 to 4.0 to 3.9. It was felt not just in San Lorenzo, but also in communities to the south of San Francisco across the bay.
Vicky Esquivel, who was at home watching TV three miles from the epicentre, told ABC 7 that “it was almost like you could feel it coming.”
BART, the Bay Area’s rapid transit system, announced later that service would be delayed by 10 minutes so that damaged rails could be inspected.
Reporter Holly Quan from KCBS Radio in Oakland said, “This was enough to make you sit up and think again.”
Her colleague Matt Bigler, who was in San Leandro, added: “I was washing dishes and all of a sudden the kitchen was moving back and forth.
An earthquake happens when two plates of the earth suddenly move past one another. The fault or fault plane is the surface where they slip.
The earthquake’s epicentre is located on the surface right above the hypocenter, whereas the hypocenter is located below the surface.
An earthquake may be preceded by tremors known as foreshocks. These smaller earthquakes happen right before a major earthquake hits the same spot.
The only way for scientists to tell if an earthquake is a foreshock is if the main event also occurs. The strongest and most significant earthquake is called the mainshock.
Main quakes are always followed by aftershocks. The epicentre of the mainshock is surrounded by a ring of smaller earthquakes.
Depending on the magnitude of the initial quake, the aftershocks could continue for weeks, months, or even years!
It isn’t that straightforward. In the event of an earthquake of any magnitude, damage will ensue.
The distance from the earthquake, the soil type, the building’s construction, and so on are all factors to consider. It is true that quakes of magnitude 4 or 5 rarely cause significant damage.