Ground surveillance and satellite map of damage to buildings after the Beirut explosion

Days after the massive explosion on August 4, 2020, in the port of Beirut in Lebanon, researchers on the ground were painting the effects of the explosion in the port and the surrounding city.

UCLA civil and environmental engineer Jonathan Stewart, who spoke about the effort at the 2021 SSA Annual Meeting, said the goal was to document and preserve data on structural and façade damage before rebuilding.

The effort also provided an opportunity to compare NASA’s Jet Propulsion Laboratory satellite surveys of the effects of the explosion with data collected from ground surveys. Stewart and colleagues concluded that satellite-based damage agent maps were effective in identifying severely damaged and undamaged buildings, but were less effective in assessing intermediate levels of structural or facade damage.

“The most important thing is that damage agent maps can certainly distinguish serious damage from no harm” for both structural and interface assessments, “but they are not good at fine tuning,” Stewart said.

“If what you care about is a fairly detailed picture of what happened, you can’t replace someone who already knows what he’s doing by looking at the structure, especially from the inside,” he added.

The Beirut Explosion Survey was organized by the Geotechnical Extreme Events Survey Association (GEER) sponsored by the National Science Foundation. In addition to Stewart and his colleagues at the American University of Beirut, the team included members from the University of Illinois and the University of Calabria in Italy. The information analyzed by the GEER team can help engineers learn more about how to build safely against similar destructive events, including earthquakes, in the future.

Stewart said their findings, which are detailed in the GEER report, “provide some recommendations on how to improve human resources when carrying out these inspections.”

That August day, a harbor fire detonated an estimated 2.75 kilotons of TNT equivalent to ammonium nitrate and fuel, an event the size of a 3.3-magnitude earthquake. Within days, Stewart said, engineers at the American University of Beirut “set up a hotline through which people could contact people interested in stabilizing the damaged structures.”

Professors and students make visits to inspect and assess the stability of these and other structures, but in-person visits were curtailed in September due to COVID-19. Next, the researchers relied on street view surveys, using GoPro 360-degree cameras mounted on cars driving around town.

Stewart said damage was graded using measures modified from those used for post-earthquake events. For example, structural damage was rated on a scale starting with minor damage to non-bearing elements until complete structural breakdown. Facade damage is graded using a scale that begins with cracked windows and extends to full blown windows and doors.

Spatial patterns of blast damage differ from those seen in an earthquake. Stewart explained that site conditions such as the base soil are more important when it comes to the structural impact of an earthquake, while the damage from the blast depends “on how you feel the explosion.” “With an explosion, the damage decreases with the distance and number of buildings between you and the explosion that may deflect its effects.”

Stewart is not an expert in explosive seismology, but has experience assessing structural damage after earthquakes from his work in post-earthquake zones with GEER. Contact a colleague at the American University of Beirut after the disaster to offer his assistance in gathering observations that could be useful to researchers and engineers in the future.

“We felt it was important to collect perishable data that we expect will be useful to people studying the effects of the explosion in urban areas, and to learn something from this disaster to improve our resilience in the face of such disasters in the future,” he said.

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