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New sensor could help buildings re-open faster after earthquakes

Following two back-to-back earthquakes in southern California, a new tool could see critical buildings re-open faster while Los Angeles has launched new initiatives to help citizens prepare.

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A new optical sensor which could dramatically speed up the re-opening of critical buildings after a major earthquake is set to be deployed in California.

 

The installation comes after two back-to-back earthquakes, of magnitude 6.4 and 7.1, in southern California earlier this month. Seismologists have warned of an increased chance of more shaking in the near future.

 

The new earthquake recovery technology, developed at Lawrence Berkeley National Laboratory (Berkeley Lab), autonomously captures and transmits data depicting the relative displacement between two adjacent storeys of a shaking building.

 

The researchers say it is able to provide reliable information about building damage immediately following an earthquake, and could expedite efforts to safely assess repair requirements and reoccupy buildings post-quake.

 

Real-world deployment

 

Scientists and engineers at Berkeley Lab, Lawrence Livermore National Laboratory and the University of Nevada-Reno began working to design an optical method of measuring ‘inter-storey drift’ within buildings in 2015. After four years of peer-reviewed research and simulation testing at the University of Nevada’s Earthquake Engineering Laboratory, the Discrete Diode Position Sensor (DDPS) will be deployed for the first time this summer in a multi-storey building at Berkeley Lab.

 

The Discrete Diode Position Sensor will be deployed for the first time this summer in a multi-storey building at Berkeley Lab.

 

The building sits adjacent to the Hayward Fault, which is considered to be one of the most dangerous faults in the United States.

 

Optical sensor

 

Measuring building inter-storey drift has been a factor in assessing buildings for post-earthquake damage for some time but finding a reliable method to do so has been challenging due to frequency limitations of sensors and the ability to receive data quickly enough to inform decision-making, as well as the cost of building accelerometer-based instrumentation.

 

DDPS leverages a promising new alternative that combines laser beams with optical sensors. The researchers have also been able to get the tool down to a quarter of the size of the original design. Further, they say the roll-out of 5G will support the required data transmission speed.

 

"Until now, there’s been no way to accurately and directly measure drift between building storeys, which is a key parameter for assessing earthquake demand in a building."

 

"Until now, there’s been no way to accurately and directly measure drift between building storeys, which is a key parameter for assessing earthquake demand in a building," said David McCallen, a senior scientist in the Energy Geosciences Division at Berkeley Lab and faculty member at the University of Nevada, who leads the research collaboration.

 

"The rigorous testing the DDPS has undergone indicates how the drift displacements measured on the three testbeds compared to representative drifts that could be achieved on an actual full-scale building undergoing strong shaking from an earthquake," he added.

 

Drift profile

 

During the earthquakes in southern California earlier this month, Ridgecrest, a city of 29,000 people, was the most populous area at the epicentre of the magnitude 7.1 earthquake which took place on July 5.

 

The quake caused water main breaks and knocked out power and communications to parts of Ridgecrest. Some buildings remained closed for up to two days. The structural damage in Ridgecrest was limited, experts say, but they note this is due to many of the city’s buildings being new and designed with resilience in mind. The situation would be much worse in a larger, older city such as Los Angeles or San Francisco, they warn.

 

The ability to measure and display key inter-storey drift information immediately after an earthquake would provide critical new data for making informed decisions on building occupancy, the Berkeley Lab researchers explain. They say that a system such as the one they have developed would provide first responders with information to help evacuate a building, and enable municipalities to keep important public buildings such as hospitals open.

 

Understanding a building’s drift profile would also allow building inspectors to inspect the most at-risk buildings first, saving a significant amount of time compared to manual inspections.

 

Risk reminder

 

McCallen said: "The major earthquakes that struck in southern California serve as a reminder of the risks associated with seismic activity across many regions of the United States. These events put an exclamation point on the need for continued societal focus on earthquake readiness and resilience, including an ability to provide the sensors and data analysis that can rapidly measure infrastructure health and inform the most effective response after the next major quake."

 

"These events put an exclamation point on the need for continued societal focus on earthquake readiness and resilience."

 

Following the quakes, Los Angeles’ Mayor, Eric Garcetti, has launched a new campaign to strengthen city-wide emergency readiness, calling on Neighbourhood Councils to appoint preparedness officers and take part in a Ready Your LA Neighborhood (RYLAN) programme.

 

In January 2019, the Mayor launched ShakeAlertLA, the US’ first publicly available earthquake early warning mobile app. The app is a collaboration with the United States Geological Survey (USGS) and provides critical seconds of warning that a major earthquake has begun and shaking is imminent — to help residents take action to protect themselves.

Many Angelenos expressed surprise that they did not receive an earthquake warning via ShaleAlertLA during the recent southern California quakes. The app was working correctly, officials say, but they are making updates based on citizen feedback.

 

The app was initially designed to issue alerts to users within Los Angeles County for earthquakes of Magnitude 5.0 or greater and a Modified Mercalli Intensity (MMI) of 4. During the recent event, the intensity did not surpass a level 3 MMI throughout most of LA.

 

The City of LA is currently working with USGS to lower the threshold to Magnitude 4.5 and an MMI of 3 by the end of July.

 

However, experts note that there is a balance to be struck between giving people important early warnings and not creating undue panic and anxiety.

 

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