A Thursday mayoral missive ordering the city to prepare for the next major earthquake contains a startling seismic statistic about when to expect the big one.
According to a statement from the Office of Mayor London Breed, “It is estimated that San Francisco has a 72 percent chance of experiencing a 6.7 magnitude or greater earthquake before 2043.”
Breed says, “We know that the next major earthquake will hit at any time and every day we should be working to prepare for it,” announcing that she is ordering city organs to “make our buildings safer now, but also [create] a comprehensive plan” for recovery in the face of an eventual disaster.
Breed’s statement appears to refer to a 2014 U.S. Geological Survey [USGS] calculation of the Bay Area’s earthquake outlook, which projected 72 percent odds of a 6.7 quake “striking somewhere in the San Francisco Bay region.”
Additionally, USGS predicts that “the probability that an earthquake of magnitude 6.0 or larger will occur before 2043 is 98 percent,” while the odds of a 7.0 or above hitting in the next 24 or so years is 51 percent.
For perspective, the USGS report puts the 1906 earthquake at 7.8 in magnitude (in the past, seismologists have pegged it at anywhere from a 7.7 to an 8.3, with 7.8 being the median of the most recent calculations) and the 1989 Loma Prieta quake at 6.9.
The most recent big quake in Napa in 2014, which killed one person, was a 6.0. The largest earthquake ever recorded on this scale was a 9.5 in Chile in 1960, which generated tsunamis that inflicted significant damage as far away as LA.
USGS bases predictions about the likelihood of future quakes partly on historical records of how frequently large (5.0 and up) earthquakes have happened in the past and how long it’s been since the last tremor, as well as on measurements of the stress currently put on active fault lines.
Breed’s executive directive orders city agencies to “strengthen the resiliency of tall buildings” and to “create a comprehensive recovery plan in preparation for the next major earthquake.”
Among the initiatives included:
- DBI and the Building Inspection Commission are tasked with developing additional regulations to address engineering issues and explore adopting higher seismic design standards.
- DEM, DBI and Public Works are assigned with updating policies for implementing safety improvements and clarifying departmental roles following an earthquake.
- The City Administrator will establish a Disaster Recovery Task Force, which will develop a recovery framework, including a comprehensive recovery plan for the Financial District and adjacent neighborhoods.
- The City Administrator will be responsible for sharing knowledge and information with other cities with tall buildings that face similar seismic risks.
Science journal Nature reported in 2018 that, based on scenarios composed after recent quakes in New Zealand and Nepal, the next major SF quake could see up to 800 casualties within minutes.
For a handy guide on earthquake preparedness, go here.