Second magnitude-4.0 earthquake to rattle Bay Area this summer is not unusual

The second magnitude-4.0 temblor to rattle the Bay Area in less than a month left San Francisco mostly unscathed Monday morning, but the quake is a reminder to always be prepared in the event of a larger event, earthquake officials said.

The quake struck at 6:49 a.m. on the Hayward Fault, the same fault that saw a magnitude-4.0 earthquake in Fremont on July 21. Monday’s quake was located in the Oakland hills, about a mile north of Piedmont, according to the U.S. Geological Survey.

Though neither of the quakes matched the magnitude-6.0 temblor that rocked Napa and much of the Bay Area nearly a year ago on Aug. 24, 2014 – the largest earthquake to hit the region since the magnitude-6.9 Loma Prieta quake struck on Oct. 17, 1989 – the two temblors serve as wake-up call that the Hayward fault is indeed active.

“Both of these earthquakes are very typical and they’re what we expect on the fault,” said AnneMarie Baltay, a seismologist with the USGS.

San Francisco residents are well-aware that an earthquake can strike at any time, particularly on the Hayward fault. In fact, there is a one in three chance that the Hayward fault will produce a magnitude-6.7 or larger temblor in the next 30 years, and earthquakes like the magnitude-4.0 on Monday don’t relieve any of that stress, according to USGS officials.

While a magnitude-4.0 earthquake may sound large, it is actually 600 or 700 times smaller than a magnitude-6.7 earthquake, Baltay said.

“We should always be worrying about earthquakes,” said Patrick Otellini, The City’s director of earthquake safety. “San Francisco has been having earthquakes for the last several thousand years. It’s just something we have to be very conscious of here.”

The City for decades has taken steps to ensure its buildings and residents will remain safe during an earth-shaking event. In 1992, shortly after the Loma Prieta quake, city officials passed the Unreinforced Masonry Building Seismic Hazard Reduction Program and Ordinance, requiring the retrofit of unreinforced masonry buildings.

Prior to that law, San Francisco had enacted the Parapet Safety Program in 1969, calling for private property owners to reinforce older parapets and roofline appendages.

However, a policy road map didn’t emerge until The City developed its Community Action Plan for Seismic Safety, an effort adopted in 2011 that aims to reduce earthquake risks in city and privately-owned buildings, as well as to develop repair and rebuilding guidelines that will accelerate the recovery after an earthquake.

More recently, city leaders in 2013 passed the Soft Story Ordinance, requiring the seismic retrofit of all wood-frame structures that have at least five residential units, three stories and were built before 1978.

Last year San Francisco passed another ground-breaking law, becoming the first city in California to require private schools to be evaluated for earthquake safety in the coming years. There is also a Façade Maintenance Program in the works, aimed at reducing the risk of façade failure in earthquakes.

“It’s still a small bite of a very large apple, but this is a great first step to start protecting San Franciscans,” Otellini said.

Other major efforts to prepare San Francisco for “the big one” included the rebuilding of the Bay Bridge and Doyle Drive to meet seismic safety standards.

The Port of San Francisco is also awaiting the results of a $500,000 earthquake vulnerability study, due by the end of the year, which will evaluate the potential weaknesses associated with earthquake hazards along the Northern Waterfront Seawall that stretches from Fisherman’s Wharf to AT&T Park, said Steven Reel, s project manager in the Port’s Engineering Division.

And earlier this year, four universities, including University of California at Berkeley, were awarded $4 million collectively from the USGS to further produce its “ShakeAlert” early earthquake warning system on the West Coast, which will ultimately give people a few seconds to take precautions before a temblor hits.

Five Steps to Be Prepared for an Earthquake or Other Emergency:

1.   Identify an out of area contact.

2.   Know your connections – who will you rely on and who will rely on you?

3.   Establish a meeting place for you and your connections.

4.   Take stock of the things you use every day that could also be useful an emergency. These are the makings of disaster supplies.

5.   Talk about what you’ve done to be prepared with people you care about.

Source: San Francisco Department of Emergency Management

EarthquakePlanningseismic safetySoft Story OrdinanceU.S. Geological Survey

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