Yesterday’s wee-hours earthquake was the largest one on the Hayward Fault for decades at 4.4 on the Richter scale. But that doesn’t mean all the tectonic energy built up in this prominent East Bay fault was released, say scientists at UC Berkeley — whose stadium sits right on the fault line.
“Although a quake with a magnitude of 4.4 can be widely felt, it is way too small to relieve the fault of the enormous mechanical stress that has accumulated there since the last really big quake on the Hayward Fault,” they write on the Berkeley Seismology Lab’s blog. On October 21, 1868, a quake several hundred times more powerful than Thursday’s struck under the city of Hayward and caused widespread damage in San Francisco and the East Bay. Its magnitude is estimated to have been almost 7 — like the destructive Loma Prieta quake of 1989, which struck on another fault.
The latest probability estimates set the chances that another deadly temblor will occur on the Hayward Fault at 30 percent in the next 30 years. Yesterday’s quake, the scientists say, was just a reminder of what’s to come.